CN101202420A - Etching top undoped intrinsic layer asymmetric metal film vertical cavity surface emitting laser - Google Patents

Abstract

The invention relates to a vertical-cavity surface-emitting laser and a preparation method for etching an asymmetrical metal film of a top non-doped intrinsic layer. It includes Bragg reflector, high resistance layer, electrode, substrate, quantum well active area. The circular metal reflective film etched on the upper surface, the metal film wire, the contact layer between the metal film and the upper electrode, and the upper electrode; the circular metal reflective film, the lower surface metal film wire, and the lower surface electrode are arranged on the lower surface of the substrate. The invention introduces the current aperture into the non-doped intrinsic layer, combines the asymmetric structure of the etched metal film on the upper surface and the surface of the substrate to realize current and light field confinement, exerts the functions of electrodes and mirrors of the metal film, and simplifies the vertical cavity The surface-emitting laser array integration process reduces the logarithm of the distributed Bragg mirror, limits the current diffusion area, improves the photoelectric coupling efficiency of the injected current, and completes the growth of the intrinsic high-resistance layer and the chip at one time, avoiding proton bombardment or oxidation separately process, which is conducive to integration.

Description

Etching top undoped intrinsic layer asymmetric metal film vertical cavity surface emitting laser

technical field

The invention relates to a semiconductor optoelectronic device, in particular to an asymmetric metal film vertical cavity surface-emitting laser for etching the top non-doped intrinsic layer.

Background technique

Vertical-cavity surface-emitting lasers (VCSELs) have recently been used in many technologies because of their low threshold, fast response, circular symmetry of emitted light, and easy two-dimensional integration. In dense wavelength division multiplexing, optoelectronic integration, optical fiber High-efficiency light sources such as communications have proved that vertical cavity surface emitting lasers have application value.

The vertical cavity surface emission structure disclosed in Chinese patent CN99253156.X includes the following contents: upper metal electrode, lower metal electrode, quantum well active layer, p+ ohmic contact layer, p-type semiconductor distributed Bragg reflector, n-type semiconductor distributed Bragg Reflector and semiconductor substrate, characterized in that the top of the quantum well active layer is a p-type semiconductor distributed Bragg reflector, the bottom is an n-type semiconductor distributed Bragg reflector, and the upper part of the metal electrode and the p-type semiconductor distributed Bragg reflector is connected to the quantum well. Well active layer, p-type semiconductor distributed Bragg reflector, p+ ohmic contact layer, etc. form a cylindrical structure; there is a lower metal electrode at the bottom of n-type semiconductor distributed Bragg reflector. The patent here is generally using the VCSEL structure.

Chinese patent CN99253155.1 relates to a dielectrically distributed Bragg reflector cavity surface emitting microcavity laser, which mainly includes a dielectrically distributed Bragg reflector, an upper electrode metal layer, a quantum well active layer, a semiconductor, and the like. The dielectric distributed Bragg reflector and the semiconductor distributed Bragg reflector are used as two reflectors in the cavity of the utility model on the upper and lower surfaces of the quantum well active layer. The upper electrode metal layer and the lower electrode metal layer are respectively made on the top of the p+ contact layer and the n ⁺ contact layer, so that the injected current does not pass through the dielectric distributed Bragg reflector and the semiconductor distributed Bragg reflector, avoiding the high resistance formed by the two, The operating current is reduced, and the heat generated by the device is reduced at the same time. This patent mentions the use of dielectric distributed Bragg reflectors and semiconductor distributed Bragg reflectors.

The Journal of Semiconductors (1993, 15(10): 700-703) reported a vertical cavity surface-emitting laser with Ag as a mirror and electrode, in which liquid phase epitaxy was used to confine the quantum well structure, and then a _SiO2 thin film protective layer was deposited at a low temperature. , use an infrared lithography machine to engrave a φ=400 micron round hole as an electrode strip limit, and then make a φ=20 micron Ag reflective surface. This document uses a metal film reflector and electrodes, but the reflectivity of the metal reflector cannot be compared with that of the semiconductor material Bragg reflector. At the same time, the electrode with φ = 20 microns cannot confine the current very well. The threshold current of the experimental test device is 3.8 amperes , and used liquid phase epitaxial growth of quantum wells and low temperature deposition of SiO ₂ two processes.

Solid State Communications (1993, 88(6): 461～463) uses liquid phase epitaxial growth to limit the quantum well structure, uses Zn diffusion platform with a diameter of 20 microns to limit the diffusion of current, and uses the top step Pd/Ge as the electrode and reflector. Mirror, the substrate metal film is the electrode. In this literature, the use of liquid phase epitaxy to study vertical cavity surface emitting lasers has been replaced by molecular beam epitaxy (MBE) or metal oxide vapor deposition (MOVCD), and the use of Zn diffusion diameter of 20 microns platform can limit the diffusion of current, but it has not reached low Threshold vertical cavity surface emission requirements, and the metal film of the substrate surface electrode is not designed to limit the shape of the current in the literature.

In the vertical cavity surface emitting laser disclosed in Journal of Vacuum Science and Technology B (1999, 17(6): 3222～3225), Au is used as the upper electrode to control the laser, but the current is controlled by bombarding the p-type Bragg mirror with protons. However, proton bombardment is difficult to achieve a current confinement region with a radius of 1 micron, and the anti-reflection coating on the surface of the substrate in this document does not play a role in confining the current.

IEEE Journal of Quantum Electronics (2003, 39 (1): 109-119) and Proceedings of SPIE (2002, 4942: 182-193) reported using the upper mirror as an electrode and a mirror to limit the current by means of an oxide layer, but respectively Oxidation is difficult to control when the radius of the current confinement region is 1 micron, and it is not easy to realize integration. Similarly, the substrate surface electrodes in this document do not play the role of confining electron flow.

The metal electrodes used in the above two patents are only components of the vertical cavity surface emitting laser, but the shape and thickness of the electrode are not involved. The distributed Bragg reflectors used in the vertical cavity surface emitting laser are more than 20 pairs of upper and lower pairs, plus The quantum well structure in the upper active region enables the composition of the material to be changed many times in the growth of the vertical cavity surface emitting laser, and the thickness of each layer is strictly controlled, which is the reason for the complex structure and harsh growth conditions of the vertical cavity surface emitting laser. . Although metal films are used as electrodes and mirrors in the above literature, due to the excessive design of the metal film, good current confinement can only be achieved by means of proton bombardment or separate oxidation. However, there are defects in proton bombardment and separate oxidation, and in the literature Emphasis is placed on the design of the metal film above and the current limiting effect of the metal film on the substrate is ignored. It is difficult to achieve a current confinement region with a radius of 1 micron by proton bombardment, and it is difficult to control the radius of 1 micron in the current confinement region by oxidation respectively, and it is not easy to realize integration.

The metal film on the upper surface can be used to form mirrors and electrodes. However, due to the inconsistency in the spatial distribution of the current and the light field, the diffusion of the current must be controlled to realize the gain waveguide control of the light field. The metal film on the top surface alone cannot realize the limitation of the current and light field at the same time. After using MBE or MOCVD to grow the main structure of the device, if other low-temperature deposition _SiO2 with higher resistivity is used as the current blocking layer, the process of the device will be increased, and the aperture size of the high-resistance area needs to be strictly demonstrated. The use of proton bombardment cannot achieve very small current apertures, and the small apertures of oxidation are uncontrollable, which will limit the development of vertical cavity surface emitting laser arrays.

Contents of the invention

The object of the present invention is to provide a vertical cavity surface emitting laser for etching the top non-doped intrinsic layer asymmetric metal film, which can overcome the deficiencies of the prior art. The present invention proposes to etch the top non-doped intrinsic layer asymmetric metal film vertical cavity surface emitting laser, that is, the shape of the upper and lower etched metal films is an asymmetric structure, and the current aperture is introduced into the non-doped intrinsic layer, combined with the above The asymmetric structure of the metal film on the surface and the surface of the substrate realizes current and light field confinement, fully exerts the functions of the metal film to increase reflectivity and limit current, improves process repeatability, and simplifies the vertical cavity surface emitting laser array integration process. The invention can reduce the logarithm of the distributed Bragg reflector, limit the current area, improve the photoelectric coupling efficiency of the injected current, complete the primary material growth of the intrinsic high-resistance layer and the chip, avoid proton bombardment or separate oxidation process, and facilitate integration.

The present invention proposes a vertical cavity surface-emitting laser with an asymmetric metal film etched top non-doped intrinsic layer, including upper and lower distributed Bragg mirrors, a high-resistance intrinsic layer, a barrier layer, an electrode, a substrate, Quantum well active region and space layer.

There is an etched circular metal reflective film on the upper surface, an etched metal film wire, and the contact layer between the etched metal film and the upper electrode and the upper electrode; the contact layer of the upper electrode and the bottom of the upper electrode are: etched circular holes Non-doped intrinsic high resistance layer, p+ type contact layer, p-type Bragg mirror, quantum well active region and space layer, n-type Bragg mirror, transition layer and substrate; etch on the lower surface of the substrate The circular metal reflective film, the metal film wire etched on the lower surface, and the electrode on the lower surface.

The radius of the circular metal reflective film on the upper surface is 4-8 microns.

The circular hole radius of the non-doped intrinsic high resistance layer is 1-2 microns.

The radius of the circular metal reflection film etched on the lower surface of the substrate is 1-2 microns.

The wires etched on the upper surface and the electrode contact layer are projected separately from the wires etched on the lower surface and the electrode contact layer on the left and right, forming an asymmetric structure.

The preparation method of the vertical cavity surface emitting laser proposed by the present invention comprises the following steps:

1) Use MBE or MOCVD on the semiconductor substrate (GaAs) at a temperature of 500°C-800°C to grow n-type Bragg mirrors, quantum well active regions, p-type Bragg mirrors, p+-type contact layers and non-doped heterogeneous intrinsic high resistance layer;

2) A circular hole is engraved in the non-doped GaAlAs intrinsic high resistance layer by photolithography;

3) Pt-Ti-Au metal film is used for p+ type contact layer of thin metal film at 400℃, and Au-Ge-Ni metal film is used for n+ type substrate;

4) Etching the upper and lower metal films by ion beams to form circular metal films, wires and electrode contact layers;

5) Divide the chip into a single laser unit to form a single laser die, or form a two-dimensional array;

6) Device packaging.

Advantage and the positive effect that the present invention produces compared with prior art:

In the non-doped intrinsic high resistance area above, the circular hole with a radius of 1-2 microns etched is combined with a circular metal mirror with a radius of 4-8 microns to form a restricted area for hole flow and improve the reflectivity of the Bragg mirror. In this way, proton bombardment and separate oxidation processes are avoided, the logarithm of Bragg mirrors is reduced, and semiconductor materials can be grown at one time by MBE or MOCVD. The metal reflector can reflect light, and the existence of the metal reflector improves the reflectivity of the light passing through the Bragg reflector. Since the above metal reflector is grown on the p-type Bragg reflector, the phase of the light is easy to control, so it can reduce the The number of pairs of Bragg reflectors can be reduced by 4 to 8 pairs for p-type Bragg reflectors. In vertical cavity surface emitting lasers, the conductive properties of the metal film must be used. A circular metal mirror with a radius greater than 10 microns cannot achieve current limitation. Reducing the size of the circular metal film can limit the current, but mirrors with a radius of less than 2 microns It is impossible to reflect all the modes in the gain waveguide. We propose to limit the current by etching a circular hole with a radius of 1-2 microns in the non-doped intrinsic layer, and improve the p-type Bragg reflection with a metal film with a radius of 4-8 microns on the circular metal film. The reflectivity of the mirror.

The circular metal film with a radius of 1-2 microns on the lower surface of the substrate, the elongated wires and the electrode contact layer form an electron flow confinement area. Electrons can enter the laser through the circular metal film, thin wires and electrode contact layer. Compared with the negative electrode in the entire substrate surface area, the present invention only has a small part of the metal film, and the electrode contact layer is far from the circular metal film. Farther away, the wire layer is slender, so the current injection area can be effectively limited. Because the substrate below is thicker and there is a certain thickness deviation, it is not appropriate to reduce the logarithm of the n-type Bragg reflector by using a metal-plated reflective film. The circular metal film on the lower surface is only used to limit the current. The n-type Bragg reflector is completed, and the metal film here also plays a certain reflection effect, but it is not as obvious as the metal film on the upper surface layer, and the size and orientation of the upper and lower metal films are asymmetric.

The metal film on the upper surface and the metal film pattern on the substrate surface have a limited size and their projections in the growth plane are separated left and right, which can effectively avoid the recombination of electrons and holes outside the central area of the active region, and improve the luminous efficiency. The non-doped intrinsic high-resistance medium etching current aperture on the device can effectively limit the current, but the other regions of the current hole in the non-doped intrinsic layer with a limited thickness still allow a small current to pass through. Under the condition of meeting the reflection transverse mode range, try to Reducing the size limit of the circular mirror on the upper surface can limit the hole diffusion area. The present invention uses upper and lower metal film electrodes and wires separated from the left and right, and the metal mirror has a limited size (one radius is 4-8 microns, and the other radius is 1-2 microns). , which can effectively reduce the recombination of electrons and holes in the area outside the concentration of the light field in the active area, and improve the photoelectric coupling efficiency.

Description of drawings

Fig. 1 is the structural representation of the product of the present invention.

Fig. 2 The top view of the upper electrode and the etched area of the top metal film of the vertical cavity surface emitting laser with etched metal film.

Figure 3 is the top view of the non-doped intrinsically high resistance region of the etching current aperture.

Figure 4. Bottom view of the etching area of the lower electrode and substrate metallized film of the vertical cavity surface emitting laser with etched metal film.

Fig. 5 is a schematic diagram of the structure of a proton bombarded vertical cavity surface emitting laser.

Fig. 6 is a structure diagram of a commonly used separately oxidized vertical cavity surface emitting laser.

Figures 7 and 8 are schematic diagrams of the structure of the upper and lower electrodes of the vertical cavity surface emitting laser after proton bombardment and oxidation respectively.

Figure 9 Threshold current curves for different lateral confinement radii.

Figure 10 Transverse Light Field Distribution Curve.

Figure 11 Threshold current density distribution curves under the lateral 2 micron confinement.

Detailed ways

The present invention is described in detail below in conjunction with accompanying drawing:

As shown in the figure, Fig. 1 is a structural schematic diagram of the product of the present invention; Fig. 2 etches the top view of the upper electrode and top layer metal film etching region of the metal film vertical cavity surface emitting laser; Fig. 3 etches the non-doped version of the current aperture The top view of the high-resistance area, and the bottom view of the etched metal film bottom electrode and substrate metal film etching area of the vertical cavity surface emitting laser in Figure 4.

Among them, 1: the circular metal reflective film etched on the upper surface, with a radius of 4 to 8 microns; 2: the metal film wire etched on the upper surface; 3: the metal film and electrode in contact with the etched electrode on the upper surface; Doped intrinsically high resistance semiconductor material, the radius of the hole is 1-2 microns; 5: p+ type contact layer; 6: p type Bragg reflector; 7: quantum well active region and space layer; 8: n type Bragg reflector ; 9: substrate; 10: circular metal reflective film etched on the lower surface, with a radius of 1-2 microns; 11: metal film wires etched on the lower surface; 12: metal film and contact with the lower electrode etched on the lower surface lower electrode.

The structure of the present invention is: the upper surface has an etched circular metal reflective film 1, an etched metal film wire 2, and the contact layer between the etched metal film and the upper electrode and the upper electrode 3, and the lower layer is sequentially: etched The non-doped intrinsic high-resistance layer 4 of the round hole, the p+ type contact layer 5, the p-type Bragg mirror 6, the quantum well active region and the space layer 7, and the n-type Bragg mirror 8, the transition layer and the lining Bottom 9, circular metal reflective film 10 etched on the lower surface of the substrate, metal film wires 11 etched on the lower surface, metal film and electrodes 12 etched on the lower surface.

Usually proton bombardment or separately oxidized vertical cavity surface emitting structure is used. Figure 5 is a schematic diagram of the structure of a proton bombarded vertical cavity surface emitting laser, in which 13: engraved round hole type upper electrode, 14: proton bombardment area, 15: the entire bottom surface lower electrode . FIG. 6 is a vertical cavity surface emitting laser structure oxidized separately, wherein 16: the upper respectively oxidized region, 17 : the lower respectively oxidized region. Figures 7 and 8 are schematic diagrams of the structure of the upper and lower electrodes of the vertical cavity surface emitting laser after proton bombardment and oxidation respectively.

We design the vertical-cavity surface-emitting laser with lateral confinement. Numerical simulation of lateral confinement affects the threshold and light field requires the following four differential equations for potential, carrier concentration, light field, and thermal field spatial coupling:

1) Voltage and current density

In a semiconductor laser, the potential distribution V satisfies the Poisson equation in cylindrical coordinates:

$\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span>}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="A20071005652300122.png,A20071005652300161.png"\; state="\{\{state\}\}">r</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span>}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="z"\; filenames="A20071005652300122.png,A20071005652300161.png"\; state="\{\{state\}\}">z</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Injection current density

$\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; J</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}<span\; class="notranslate">\; \&dtri;</span>\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

where ρ is the resistivity of the semiconductor material.

2) Carrier concentration

The carrier concentration distribution plays an important role in the behavior of gain semiconductor lasers. According to the continuity equation of electrons and holes, the non-equilibrium carriers in the active region of semiconductor lasers in steady state satisfy:

${\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{<span\; class="notranslate">\; \&dtri;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; BN</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}{<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; hv</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; J</span>}}{\mathrm{<span\; class="notranslate">\; ed</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

where D _n , B, τ _s , d, J are diffusion coefficient, spontaneous emission recombination coefficient, carrier lifetime, active layer thickness and active region current density, g(N(r)) is gain, P _a is the average optical power in the cavity:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&pi;s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{<span\; class="notranslate">\; \&Integral;</span><span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="act"\; filenames="A20071005652300122.png,A20071005652300161.png"\; state="\{\{state\}\}">act</figure-callout></span>}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; c</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; \&psi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; dxdy</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Here s is the lateral radius of the active region. Gain g(N,T):

g(N,T)=a(T)[N(r)-N _th ](5)

Among them, N(r) is the carrier concentration distribution in the active region, and N _th is the transparent carrier concentration. From the experimental data, it can be assumed that the gain coefficient a(T) varies linearly with temperature,

a(T)=b-ξ(TT ₀ )(6)

Here, b=4.12×10 ^-16 cm ² , ξ=7.0×10 ^-19 cm ² /K.

3) Light field distribution

The light wave of the laser satisfies Maxwell's equations, and the intensity of the light field in cylindrical coordinates can be written as:

E(r, θ, z) = ψ(r) φ(θ) exp(-iβ _z z) (7)

Among them, β _z is the propagation constant in the z direction,

$\mathrm{\&phi;}\left(\mathrm{\&theta;}\right)=\frac{1}{\sqrt{2\mathrm{\&pi;}}}{e}^{\mathrm{im\&theta;}},$ m=0, ±1, ±2, ... (8)

where ψ(r) satisfies:

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}\frac{<span\; class="notranslate">\; \&PartialD;</span>}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; \&psi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="k"\; filenames="A20071005652300162.png"\; state="\{\{state\}\}">k</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&psi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

4) Thermal field distribution

According to the actual cylindrical symmetrical structure of the laser, and assuming that the temperature is continuously distributed at the interface of any two layers, there is no heat loss on the top and side of the laser, and the heat flows to the heat sink. The heat conduction equation is:

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}\frac{<span\; class="notranslate">\; \&PartialD;</span>}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; T</span>}}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="z"\; filenames="A20071005652300122.png,A20071005652300161.png"\; state="\{\{state\}\}">z</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&kappa;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

Q _i (r, t) represent the heat flux density of the active region, the two cladding n-type and p-type DBR layers and the substrate layer, respectively.

We use the finite difference method (FDM) and the matrix eigenvalue method to solve the self-consistent solution of the above equation (Zhao Hongdong, et al. The influence of potential on the threshold of vertical cavity surface emitting laser in n-type DBR. Acta Physica Sinica, 2004(11): 3744- 3747). First, the equation (1) (3) (9) (10) is discretized by the finite difference method, and then the equation (9) is transformed into a problem of solving algebraic eigenvalues, and a stable solution is obtained through self-consistent calculation. The physical parameters used in the calculation See Table 1. The threshold current curve at the lateral confinement radius, the lateral light field distribution curve and the lateral current density distribution curve are numerically calculated by the above equation (see FIGS. 9, 10, 11).

Table.1 Selection of physical parameters

Figure 9 shows the threshold current curves under different lateral constraints, indicating that the threshold value is the lowest near 2 microns. Since some current will leak from the intrinsic layer through the wire and electrode solder joints, the upper surface intrinsic layer current hole and the lower surface The surface electrodes are suitably smaller, designed to be 1-2 microns respectively. According to Figure 10, it can be seen that the radius of the light field is about 6 microns, and at the same time, the effect of limiting the current is taken into account. Therefore, the radius of the metal mirror on the upper surface is designed to be 4-8 microns, and the current density distribution in the active area is shown in Figure 11, which can reach limiting current action.

Common vertical cavity surface emitting laser structure manufacturing process (Jumal of Vacuum Science and Technology B (1999, 17 (6): 3222 ~ 3225; IEEE Journal of Quantum Electronics (2003, 39 (1): 109-119) and Proceedings of SPIE ( 2002, 4942: 182-193): After using MBE (molecular beam epitaxy) or MOCVD (metal oxide vapor deposition) to grow n-type Bragg mirrors, quantum well active regions and p-type Bragg mirrors on semiconductor substrates, Lateral current confinement is formed by proton bombardment or oxidation respectively (Figure 5, 6), and then the round hole electrode and the entire lower surface electrode are fabricated on the upper surface by deposition and photolithography (Figure 7, 8), and finally the device is packaged.

In the present invention, growing n-type Bragg emitting mirror, quantum well active region, and p-type Bragg reflecting mirror are the same as the conventional method, but adding a non-doped intrinsic high-resistance layer, engraving a current aperture in this layer, and growing It is necessary to coat the upper surface and the lower surface of the device with a metal reflective film, and etch the upper and lower asymmetrical circular mirrors, wires, and the contact layer of the electrodes, and finally deposit the upper and lower electrodes.

The radius of the current hole in the non-doped intrinsic high-resistance region of the present invention is 1 to 2 microns, and the projections of the wires and electrodes on the upper and lower surfaces should be on a straight line, but they are separated left and right by the center point of the device, but the shape is asymmetrical, that is, the upper surface The radius of the circular metal reflector is 4-8 microns, the radius of the circular metal film on the lower surface of the substrate is 1-2 microns, the thickness is on the order of nanometers, and the wires are as thin as possible when the resistance value is satisfied.

Taking the III-V GaAs-AlGaAs vertical cavity surface emitting laser as an example, the metal film etching vertical cavity surface emitting laser is realized through the following process, and the manufacturing process of the vertical cavity surface emitting laser of other materials is the same except that the semiconductor material is different. .

Using MOCVD on the semiconductor substrate, the temperature is 500 ℃ ~ 800 ℃ (choose 600 ℃) to grow n-type Bragg reflectors, quantum well active regions, p-type Bragg reflectors, p+-type contact layers and non-doped itself. Sign GaAlAs high resistance layer. The substrate is GaAs, the n-type and p-type are realized by GaAs-AlGaAs doped with Si and Zn respectively, the quantum well is GaAs, and the barrier layer is AlGaAs material.

A circular hole is etched in the non-doped GaAlAs intrinsic high resistance layer by photolithography.

Pt-Ti-Au metal film is used for the p+ type contact layer of the thin metal film plated at 400°C, and Au-Ge-Ni metal film is used for the n-type substrate.

The upper and lower metal films are etched by ion beams to form circular metal films, wires and electrode contact layers.

The chip is divided into several laser units to form a single laser die, or into a two-dimensional array (eg, 20×20).

Device packaging is carried out in the usual way.

During the material growth process, the growth equipment can strictly control the growth thickness, and the device can be tested by using an ordinary semiconductor laser characteristic tester.

In the present invention, the insulating layer with a circular hole radius of 1-2 microns in the non-doped intrinsic high-resistance area on the upper surface of the device limits the hole flow, and the metal mirror with a growth radius of 4-8 microns on the upper surface increases the reflectivity at the same time The current area is limited to a certain extent, but the thickness meets the laser transmission requirements. On the other hand, the circular metal film on the lower surface of the substrate has a radius of 1-2 microns, which limits the current and light waves again. Therefore, the etching of intrinsic high-resistance areas and mirrors is used to achieve the effects of limiting current and increasing light reflectivity.

Compared with the proton bombardment vertical cavity surface emitting laser, the present invention avoids the proton bombardment process, and the proton bombardment will cause passing damage and increase the absorption of materials, which is not conducive to lowering the threshold value of the laser. Compared with oxidizing vertical cavity surface emitting lasers separately, it is difficult to precisely control the oxidation when the radius is 1 micron, and the process repeatability is poor. However, the present invention uses a photolithography process. Now the etching technology has reached 0.1 micron, so it can accurately etch small The metal film has good process repeatability and can form industrial production.

The present invention uses the top non-doped intrinsic layer as the hole-limiting layer. Compared with the use of MBE to grow the chip, if the conventional process is used to deposit _SiO with high resistivity at low temperature to become the current blocking layer, the insulating material needs to be placed on other The re-growth process in the equipment, the non-doped intrinsic semiconductor material of the present invention can be completed at one time by MBE or MOCVD and quantum well Bragg mirror, etc., reducing the process of growing _SiO2 layer.

The present invention utilizes the introduction of a metal film on the p-type Bragg reflector to increase the reflectivity, and at the same time estimates the upper limit of the reflectivity of a single metal film. Therefore, the combination of the Bragg reflector and the metal film can meet the requirements of the reflectivity at the top of the vertical cavity surface emitting laser. Require.

On the surface of the substrate, no non-doped high-resistance semiconductor is used to etch the aperture to limit the current, but by etching the metal film pattern up and down with a limited size and a structure that separates the two sides of the projection, secondary epitaxy can be avoided, because MBE or MOCVD cannot simultaneously Depositing material on both sides of the substrate necessitates repositioning the chip, so the invention again saves the process.

Briefly illustrate the working principle of the present invention according to the accompanying drawings.

The holes injected by the upper electrode flow through the p-type Bragg reflector through the etched aperture, and then reach the active area to recombine with the electrons passing through the substrate and the n-type Bragg reflector from the lower electrode to generate spontaneous emission photons and stimulated emission. The flow of photons and holes is limited by the circular current aperture of the etched non-doped intrinsic layer, and the flow of electrons is respectively limited by the circular metal film. The holes and electrons flowing into the wires and electrodes must recombine in the area close to the central axis , thus improving the compounding efficiency. Photons are reflected by the p-type Bragg reflector and the metal reflector above, return to the active area to be amplified, propagate to the n-type Bragg reflector for reflection, and then return to the active area. When the light gain in the active region can compensate for the loss of light output, reflective mirrors and materials during propagation, the laser achieves dynamic equilibrium. The metal mirror etched on the upper surface can increase the reflectivity, the non-doped intrinsic layer is etched on the upper surface to limit the injection current, the circular metal film on the surface of the substrate limits the electron injection area, and the electrodes are distributed around the axis of the device to reduce the weak The recombination of the light field area improves the coupling efficiency.

Claims (7)

1. the asymmetric metal membrane vertical cavity surface-emitting laser of etching top end non-doping intrinsic layer comprises upper and lower distribution Bragg mirror, resistive formation, and barrier layer, electrode, substrate, quantum well active area and space layer is characterized in that:

Upper surface has the circular metal reflectance coating (1) of etching, metal film lead (2) and the metal film of etching and the contact layer and the top electrode (3) of top electrode of etching; The contact layer of top electrode and top electrode (3) below is followed successively by: the non-doping intrinsic resistive formation (4) of etching circular hole, p+ type contact layer (5), p type Bragg mirror (6), quantum well active area and space layer (7), n type Bragg mirror (8), transition zone and substrate (9); Circular metal reflectance coating (10), the metal film lead (11) of lower surface etching, lower surface electrode (12) in the lower surface etching of substrate (9).

2. vertical cavity surface emitting laser according to claim 1 is characterized in that the radius of the circular metal reflectance coating (1) of described upper surface is 4～8 microns.

3. vertical cavity surface emitting laser according to claim 1, the circle hole radius that it is characterized in that described non-doping intrinsic resistive formation (4) is 1～2 micron.

4. vertical cavity surface emitting laser according to claim 1 is characterized in that the radius of the circular metal reflectance coating (10) of described substrate lower surface etching is 1～2 micron.

5. vertical cavity surface emitting laser according to claim 1 is characterized in that lead, the projection of contact electrode layer position of lead, contact electrode layer and the lower surface etching of upper surface etching divided right and left, and becomes unsymmetric structure.

6. the preparation method of vertical cavity surface emitting laser according to claim 1 is characterized in that it may further comprise the steps:

1) use MBE or MOCVD on Semiconductor substrate, temperature is 500 ℃-800 ℃ in turn growing n-type Bragg mirror, quantum well active area, p type Bragg mirror, p+ type contact layer and non-doping intrinsic resistive formations;

2) carve circular port by photoetching method in the non-doped with Al As intrinsic resistive formation;

3) 400 ℃ of thin metal film p+ type contact layers of plating use and use the Au-Ge-Ni metal film on Pt-Ti-Au metal film, the n+ type substrate;

4) form circular metal film, lead and contact electrode layer by the upper and lower metal film of ion beam etching;

5) chip is divided into single laser element, forms single laser tube core, or becomes two-dimensional array;

6) device package.

7. the preparation method of vertical cavity surface emitting laser according to claim 6 is characterized in that described substrate is GaAs.

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