CN114865456A - Dual-wavelength quantum cascade laser chip and dual-wavelength emission method - Google Patents

Abstract

The invention discloses a dual-wavelength quantum cascade laser chip and a dual-wavelength emission method; the chip includes a plurality of wavelength devices, an upper cladding layer and a lower cladding layer; each wavelength device includes m double-doped superlattices; Each double-doped superlattice includes n superlattice units; the first superlattice unit included in each double-doped superlattice is the active region, and the remaining n-1 superlattice units is the injection area; the upper cladding layer and the lower cladding layer are located above and below the multiple wavelength devices respectively; the upper cladding layer and the lower cladding layer work together to confine electrons in the active area of the multiple wavelength devices; through the chip Two wavelengths can be emitted at the same time, and the production process of the chip is relatively simple.

Description

A dual-wavelength quantum cascade laser chip and dual-wavelength emission method

technical field

The invention belongs to the field of optoelectronic chips, in particular to a dual-wavelength quantum cascade laser chip and a dual-wavelength emission method.

Background technique

In the mid- and far-infrared bands, there are mainly two low-absorbing atmospheric windows, which are 3-5 μm and 8-12 μm, respectively. Among them, the 3μm ~ 5μm band has very considerable application prospects in military infrared countermeasures, explosive monitoring, environmental pollution monitoring, and terahertz imaging. The 8-12μm infrared band is the atmospheric window for many new aircraft reconnaissance and missile guidance penetration; in addition, the characteristic spectrum of jet engine tail flame is near the medium and long wavelengths, and detectors working in this band are widely used in the guidance of infrared guided missiles.

The initial QCL requirements for infrared countermeasures are mainly in the 3-5 μm band. Today, advanced infrared guidance detectors are developing in the direction of mid- and long-wave composite guidance. In order to effectively cope with this trend, the infrared photoelectric countermeasure system must also use the mid- and long-wave dual-band laser accordingly. At present, there is no infrared countermeasure technology that emits two wavelengths from a single chip, but the United States has carried out research on medium- and long-wave composite interference infrared light sources, while this technology in my country is still blank. Therefore, the development of an infrared countermeasure technology that emits two wavelengths from a single chip has become an indispensable part of the work of relevant technology researchers in my country.

If the infrared photoelectric countermeasure system adopts the mid- and long-wave dual-band laser, then higher technical requirements are put forward for the long-wave high-power infrared quantum cascade laser chip. However, the current 8-12μm band semiconductor laser chips cannot reach the output power and beam quality required by the directional infrared countermeasure system (DIRCM). The development of high-power long-wave quantum cascade laser chips has been lagging behind in the mid-infrared band. The main reasons are as follows: First, the lifetime of the upper lasing level decreases rapidly with the increase of wavelength, which makes population inversion more difficult; Second, the long-wave energy is lower, the energy level interval is smaller, and the leakage from the injection energy level to the low lasing energy level increases significantly; third, the waveguide loss due to the absorption of free carriers is proportional to the square of the wavelength, Therefore, long-wave lasers will have higher waveguide losses.

The popular material system for mid- and far-infrared quantum cascade laser chips is the InGaAs/InAlAs material system grown on the InP substrate. When designing quantum cascade laser chips, there are two lines of thought. The first idea is strain compensation. That is, when growing an InGaAs/InAlAs material system, if you want to grow a good material, you first need to grow a material system that matches the lattice of the InP substrate. The lattice constant of InGaAs is larger than that of the substrate, and the lattice constant of InAlAs is smaller than that of the substrate. In theory, through strain compensation, the mismatch degree of the entire material can be almost zero. However, quantum cascade lasers often have hundreds of layers of materials, and the lattice constant of each layer is different from that of the substrate, so the growth process cannot be effectively controlled, that is, the overall stress accumulation cannot be minimized, resulting in quantum cascades. The actual growth process of the laser chip becomes very complicated. The second idea is the two-phonon resonance relaxation of the low-energy state electrons. That is, in the two-phonon resonance scheme, the upper and lower energy levels of the laser determine the lasing wavelength. There are two energy levels below the laser energy level, and the energy level difference between these three energy levels is the energy of one longitudinal optical phonon. After two relaxations of longitudinal optical phonons, the lifetime of the low-energy electrons will be greatly reduced, and the population inversion efficiency will be very high. However, in the two-phonon resonance, it is necessary to strictly design the energy level difference, not only the flexibility of wavelength design is not high, but also the energy band tailoring is difficult.

Therefore, how to make a single laser chip emit two wavelengths at the same time, simplify the growth process of the quantum cascade laser chip, and improve the flexibility of the adjustment of each energy level difference in the two-phonon resonance has become a key issue in current research.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention provides a dual-wavelength quantum cascade laser chip and a dual-wavelength emission method that solves at least some of the above-mentioned technical problems. The chip can emit two wavelengths at the same time, and the production process of the chip is relatively simple.

On the one hand, an embodiment of the present invention provides a dual-wavelength quantum cascade laser chip, comprising a plurality of wavelength devices, an upper cladding layer and a lower cladding layer;

Each of the wavelength devices includes m double-doped superlattices; each of the double-doped superlattices includes n superlattice units;

In each of the double-doped superlattice, the first superlattice unit included is an active region, and the remaining n-1 superlattice cells are an implantation region;

The upper cladding layer and the lower cladding layer are respectively located above and below the plurality of wavelength devices; the upper cladding layer and the lower cladding layer work together to confine electrons in the active regions of the plurality of wavelength devices .

Further, a cap layer is also included; the cap layer is located above the upper cladding layer for reducing ohmic contact resistance.

Further, the upper cladding layer, the lower cladding layer and the cap layer are all made of InP material.

Further, a concave isolation groove is provided in the middle of any two adjacent wavelength devices.

On the other hand, an embodiment of the present invention also provides a dual-wavelength emission method, which is applied to the above-mentioned dual-wavelength quantum cascade laser chip; the method includes:

S1. For each double-doped superlattice, the first superlattice unit included in it is used as an active region, and the remaining n-1 superlattice cells included in it are used as an implantation region; and Each of the superlattice cells satisfies a Poisson distribution equation;

S2, respectively combining the active regions and the implanted regions corresponding to the m double-doped superlattices to obtain an integrated active region and an integrated implanted region;

S3, injecting currents of different intensities into the integrated injection region according to a preset rule to generate corresponding electric field differences in multiple regions of the integrated active region;

S4. Based on the electric field difference, obtain the lasing wavelength through calculation.

Further, in the S1, the Poisson distribution equation is expressed as:

Among them, V represents the electric potential; V _s represents the equivalent velocity of electrons; q<V _S > represents the potential energy; ρ _L represents the resistivity, _xi represents the starting coordinate value of the i-th double-doped superlattice; ε represents dielectric constant; e represents unit charge; e<v _s > represents electron potential energy; J _e represents current density within the double-doped superlattice; Nd ⁺ represents donor ion concentration; _Nd (x) represents coordinate x position Donor ion concentration at ; L represents the length of a double-doped superlattice.

Further, in S3, the length of each of the double-doped superlattice regions is set as L; the doping concentration of the active region in each of the superlattice units is set as Nd ₁ , The doping concentration of the implanted region in each superlattice unit is set as N _d2 , and N _d1 >N _d2 ; based on this, the formula (2) can be used to obtain:

where n represents a positively charged donor ion in the double-doped superlattice region;

By integrating the charge density on the jth superlattice unit in the double-doped superlattice, the jth superlattice unit and the j+1th superlattice in the double-doped superlattice are obtained. The electric field difference between lattice cells; the electric field difference is expressed as:

where l represents the length of one unit superlattice.

Further, the S4 specifically includes:

S41. Based on the electric field difference, the optical transition energy is obtained by calculation; the corresponding calculation formula is expressed as:

ΔE _OT =αΔF+β (5)

Among them, ΔE _OT represents the optical transition energy; α and β both represent the superlattice cell fitting constant;

S42. Based on the optical transition energy, the lasing wavelength is obtained by calculation; the corresponding calculation formula is expressed as:

where λ represents the lasing wavelength.

Compared with the prior art, a dual-wavelength quantum cascade laser chip described in the present invention has the following beneficial effects:

(1) Composed of the same superlattice unit SLC, but integrating alternate doping into a single SL stack, the homogeneous active region greatly reduces the difficulty of material growth and makes it easier to obtain higher material film quality and interface quality.

(2) A double-doping approach is used for all superlattice cell SLCs to generate different electric fields at specific injection current strengths, resulting in a single SL stack with multiple optical transitions. The optical transition energy difference is proportional to the applied electric field difference, and the electric field difference is determined by the double doping, so the light energy can be adjusted by changing the doping.

Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description, claims, and drawings.

The technical solutions of the present invention will be further described in detail below through the accompanying drawings and embodiments.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the specification, and are used to explain the present invention together with the embodiments of the present invention, and do not constitute a limitation to the present invention. In the attached image:

FIG. 1 is a structural diagram of a dual-wavelength quantum cascade laser chip provided by an embodiment of the present invention.

FIG. 2 is a schematic structural diagram of a wavelength device according to an embodiment of the present invention.

Detailed ways

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be more thoroughly understood, and will fully convey the scope of the present disclosure to those skilled in the art.

Referring to FIG. 1 , an embodiment of the present invention provides a dual-wavelength quantum cascade laser chip, which starts from a substrate and grows from a lower mesh, and sequentially includes: a lower cladding layer, a plurality of wavelength devices, an upper cladding layer and a cap layer;

Among them, two wavelength devices are provided in the embodiment of the present invention, and each wavelength device includes m double-doped superlattice D ² SLS (Dual Doping Super Lattice Stack), and m is usually 25 to 35 periods. For details, see As shown in Figure 2; each double-doped superlattice D ² SLS includes n superlattice cells SLC (Super lattice cell); the double-doping method is adopted for each superlattice cell SLC, that is, for a single double-doped superlattice cell SLC In terms of the doped superlattice D ² SLS structure, the doping concentration of the first superlattice unit SLC included in it is set to N _d1 , and it is used as the active region; the remaining n-1 superlattices The doping concentration of the unit is N _d2 , and it is used as the injection region; the Poisson distribution equation is satisfied between each superlattice unit SLC to ensure that the cascade of carriers can be realized; multiple D ² SLSs are integrated into a In the source region, different electric fields will be generated in different regions of the active region under a specific injection current intensity. By designing the doping distribution of D ² SLS, a certain value of electric field difference ΔF can be obtained; different electric field differences ΔF correspond to different optical The transition energy difference ΔE _OT ; the electric field difference ΔF determines the optical transition energy difference ΔE _OT , thereby achieving a specific lasing wavelength λ. Compared with the active region of two-phonon resonance, the double-doped superlattice active region adopted in the embodiment of the present invention can greatly improve the flexibility of device design.

Referring to Table 1 below, in the embodiment of the present invention, the lower cladding layer of the chip is an InP substrate with a thickness of 500 μm, and Core 1 and Core 2 are both double-doped active regions, corresponding to wavelengths of 4.6 μm and 8.5 μm respectively; It is a 3μm-thick InP material, and the upper and lower cladding structures work together to effectively confine electrons in the active region, and at the same time play a role in light confinement; the last layer of epitaxy material is a 1μm-thick InP cap layer structure, and the cap layer structure is highly doped It helps the electrodes to form a good ohmic contact and reduces the ohmic contact resistance; the lattice-matched InGaAs/InAlAs/InP material is used in the embodiment of the present invention, which can avoid the problems caused by the strain compensation technology;

Table 1

After the epitaxial growth is completed, the chip processes such as mesa etching, DBR etching, substrate thinning, and electrode deposition are performed to obtain the monolithic integrated tapered waveguide with dual-distributed Bragg reflector (Dual-DBR) shown in Figure 1. The dual-wavelength near-diffraction-limited quantum cascade laser chip, in which the two DBRs are Bragg gratings with lasing wavelengths of 4.6 μm and 8.5 μm respectively, and the gratings are used as additional mode filters to achieve stable dual-wavelength output; the isolation groove allows the two wavelengths to be output. The electrical insulation between the device structures can apply different current injections to the two wavelength chip structures of 4.6μm and 8.5μm, thereby realizing the function of simultaneously or separately outputting two wavelengths of laser light; the emitted light of the ridge waveguide (RW) is monolithically coupled In the tapered structure as power amplification, the tapered structure plays the role of power amplification. The chip adopts a double-doped active area structure and an isolation trench structure, and can output 4.6±0.5μm and 8.5±0.5μm lasers simultaneously or separately. In military infrared countermeasures, the output of 4.6μm or 8.5μm can be selected according to the wavelength of the opponent's missile, and even a single chip can be used to fight missiles with two different target wavelengths.

The embodiment of the present invention also provides a dual-wavelength emission method, which is applied to the above-mentioned dual-wavelength quantum cascade laser chip; the method includes:

S1. For each double-doped superlattice, the first superlattice unit included in it is used as the active area, and the remaining n-1 superlattice units included in it are used as the implantation area; and each The superlattice cells satisfy the Poisson distribution equation;

S2, respectively combining the active regions and the implanted regions corresponding to the m double-doped superlattices to obtain an integrated active region and an integrated implanted region;

S3, injecting currents of different intensities into the integrated injection region according to a preset rule to generate corresponding electric field differences in multiple regions of the integrated active region;

S4, based on the electric field difference, obtain the lasing wavelength through calculation.

Each of the above steps will be described in detail below.

In the above step S1, the Poisson distribution equation is expressed as:

Among them, V represents the electric potential; V _s represents the equivalent velocity of electrons; q<V _S > represents the potential energy; ρ _L represents the resistivity, _xi represents the starting coordinate value of the i-th double-doped superlattice; X represents the Taking the substrate as the starting point, the epitaxial direction is the positive one-dimensional coordinate; ε represents the dielectric constant; e represents the unit charge; e<v _s > represents the electron potential energy; J _e represents the current in the double-doped superlattice Density; Nd ⁺ represents the donor ion concentration; _Nd (x) represents the donor ion concentration at the coordinate x position; L represents the length of 1 double-doped superlattice.

In the above step S3, the length of each double-doped superlattice region is set to L; the doping concentration of the active region in each superlattice unit is set to Nd ₁ , and each superlattice unit is set to The doping concentration of the implanted region in is set to N _d2 , and N _d1 >N _d2 ; based on this, in order to simplify the derivation, it is considered that _Je , ε, and ν _s are constants. Substituting the double doping concentration and the length of the doped region into equation (2), we get:

where n represents a positively charged donor ion in the double-doped superlattice region;

Under an applied bias voltage, the negative electron flow makes the intrinsic region of all SLCs negatively charged, which results in a sawtooth periodic distribution of the electric field in the D ² SLS. By integrating the charge density on the jth superlattice unit SLC in the double-doped superlattice, in the double-doped superlattice D ² SLS, the jth superlattice unit SLC and the jth superlattice unit SLC are obtained. The electric field difference ΔF between j+1 superlattice cells SLC; the electric field difference ΔF is expressed as:

where l represents the length of one superlattice unit.

In the above step S4, in the above formula (4), since the SLC has periodicity, the integration limit x _i +(j-1)* can be set to 0. It can be seen from formula (4) that among the i-th D ² SLS, from the 2nd SLC to the n-th SLC, and from the 2nd SLC to the (i+1)-th D ² SLS from the 1st SLC , the electric field difference ΔF is constant and independent of the SLC sequence, ie the electric field of adjacent active regions decreases linearly along these SLCs. Tunable optical transition energies EOT can be achieved when the SL region is biased under different electric fields:

ΔE _OT =αΔF+β (5)

Among them, α and β are the constant parameters of the SLC design, and the electric field variation is ΔF. The corresponding optical transition energy difference ΔE _OT =αΔF will be obtained by applying different electric field variation ΔF. By designing the doping distribution of D ² SLS, a certain value of electric field variation ΔF can be obtained. According to formula (5), different E _OTs in each SLC can be realized with constant space energy ΔE _OT . Therefore, through each SLC Different E _OTs in SLC can obtain broad and flat gain spectrum in mid-infrared and terahertz bands. In short, the optical transition energy difference is proportional to the applied electric field difference, and the electric field difference is determined by the double doping, so by changing the doping, the light energy can be adjusted, and then the wavelength corresponding to the laser chip can be changed. The calculation formula corresponding to the lasing wavelength is expressed as:

where λ represents the lasing wavelength.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Thus, provided that these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims (8)

1. A dual-wavelength quantum cascade laser chip is characterized by comprising a plurality of wavelength devices, an upper cladding and a lower cladding;

each of the wavelength devices comprises m double-doped superlattices; each of the double-doped superlattices comprises n superlattice units;

each double-doped superlattice comprises 1 st superlattice unit serving as an active region and the rest n-1 superlattice units serving as injection regions;

the upper cladding layer and the lower cladding layer are respectively positioned above and below the plurality of wavelength devices; the upper and lower cladding layers cooperate to confine electrons to an active region of the plurality of wavelength devices.

2. The dual wavelength quantum cascade laser chip of claim 1, further comprising a cap layer; the cap layer is positioned above the upper cladding layer and used for reducing ohmic contact resistance.

3. The dual wavelength quantum cascade laser chip of claim 2, wherein the upper cladding layer, the lower cladding layer and the cap layer are all InP material.

4. The dual wavelength quantum cascade laser chip of claim 1 wherein a concave isolation trench is provided between any two adjacent wavelength devices.

5. A dual wavelength emission method, applied to the dual wavelength quantum cascade laser chip of any one of claims 1 to 4; the method comprises the following steps:

s1, for each double-doped superlattice, taking the 1 st superlattice unit included in the double-doped superlattice as an active region, and taking the remaining n-1 superlattice units included in the double-doped superlattice as an injection region; each superlattice unit meets a Poisson distribution equation;

s2, respectively combining the active regions and the injection regions corresponding to the m double-doped superlattices to obtain an integrated active region and an integrated injection region;

s3, injecting currents with different intensities into the integrated injection region according to a preset rule, and generating corresponding electric field differences in a plurality of regions of the integrated active region;

and S4, obtaining the lasing wavelength through calculation based on the electric field difference.

6. The dual wavelength transmission method of claim 5 wherein in said S1, said poisson distribution equation is expressed as:

wherein V represents an electric potential; v _s Represents the equivalent velocity of the electrons; q. q.s<V _S >Representing the potential energy; rho _L Denotes resistivity, x _i Representing the initial coordinate value of the ith double-doped superlattice; ε represents a dielectric constant; e represents a unit charge; e.g. of the type<v _s >Represents the electronic potential energy; j. the design is a square _e Represents the current density within the double doped superlattice; nd (neodymium) ⁺ Represents the donor ion concentration; n is a radical of _d (x) Representing the concentration of donor ions at the x-position of the coordinate; l represents the length of 1 double doped superlattice.

7. The dual wavelength transmission method as claimed in claim 6, wherein in said S3, the length of each of said double doped superlattice regions is set to L; setting the doping concentration of the active region in each superlattice unit as Nd ₁ Setting the doping concentration of the implantation region in each superlattice cell to be N _d2 And N is _d1 >N _d2 (ii) a Based on this, it can be obtained by the formula (2):

wherein n represents positively charged donor ions within the double doped superlattice region;

obtaining the electric field difference between the jth superlattice unit and the (j +1) th superlattice unit in the double-doped superlattice by integrating the charge density on the jth superlattice unit in the double-doped superlattice; the electric field difference is expressed as:

where l represents the length of one superlattice cell.

8. The dual-wavelength transmitting method of claim 7, wherein the S4 specifically includes:

s41, obtaining optical transition energy through calculation based on the electric field difference; the corresponding calculation formula is expressed as:

ΔE _OT ＝αΔF+β (5)

wherein, Delta E _OT Represents the optical transition energy; both α and β represent superlattice cell fitting constants;

s42, acquiring the lasing wavelength through calculation based on the optical transition energy; the corresponding calculation formula is expressed as:

where λ represents the lasing wavelength.

Images