RU2548610C2 - WHITE GLOW LED AND LED HETEROSTRUCTURE BUILT AROUND SOLID-STATE SOLID GaPAsN SOLUTIONS OF GaP AND Si SUBSTRATES - Google Patents

Abstract

FIELD: physics, optics.

SUBSTANCE: white glow LED comprises n-type semiconductor ply composed of semiconductor solid solution GaP_1-x-yAs_xN_y (0.3>x>0, 0.030>y>0.004), heterostructure with inherent conductivity type composed by semiconductor solid solutions GaP_1-x-yAs_xN_y (0.3>x>0, 0.030>y>0.004) composed above ply of n-type semiconductor, ply of semiconductor GaP_1-x-yAs_xN_y (0.3>x>0, 0.030>y>0.004) of p-type composed on heterostructure GaP_1-x-yAs_xN_y (0.3>x>0, 0.030>y>0.004) with inherent conductivity type and final thin metamorphic ply of semiconductor InGaAs of p-type. Note here that molar portions of nitrogen, y, and arsenic, x, either simultaneously abruptly vary or individually in the range of 0.3>x>0 and 0.030>y>0.004 to form graded band-gap semiconductor material. Invention covers also the heterostructure emitting white light.

EFFECT: higher efficiency of the use of p-n-junctions, LEDs with increased light flux and power.

15 cl, 4 dwg

Description

Technical field

The invention relates to white LEDs, which are semiconductor optoelectronic devices, and methods for manufacturing such optoelectronic devices. Light emitting diodes are widely used in optical information display devices, traffic lights, communication systems, lighting devices and medical equipment.

State of the art

Currently, white LEDs are usually made in three main ways.

The first method involves placing three separate LED crystals emitting red, green and blue light (RGB) in one LED housing. The combination of emissions of red, green and blue gives a white glow.

The second method, which is currently widely used for the manufacture of white LEDs, involves the use of a single GaN-based LED crystal emitting in the blue or ultraviolet range, coated with a fluorescent material, a phosphor, or an organic dye. It should be noted that the conversion of blue or ultraviolet radiation to longer wavelengths of the visible range by fluorescent material leads to energy loss.

The third method of manufacturing, the closest to the present invention, white LEDs was investigated S.-U. Chen (C.-Yu. Chen) et al. (US Pat. No. 6,163,038). This patent describes a white light emitting diode and a method for manufacturing a white light emitting diode, which itself can emit white light due to the presence of at least two forbidden energy zones in the crystal structure of this light emitting diode. This technology uses Multiple Quantum Well (MQWs) emitting light of different colors to produce white light. MQWs are formed by adjusting the parameters of the epitaxial process. However, the patent does not specify how this is achieved. In the course of research S.-U. Chen et al. Managed to realize an LED crystal with an MQW, the emission spectrum of which contains many peaks, which are then combined to produce a white glow. Using the proposed method, S.-U. Chen et al. Failed to produce a crystal with an MQW, with a continuous spectrum that spans the entire visible range.

Another variant of the third method and the associated LED manufacturing technology was proposed by S.J. Chua (SJ Chua) and others (US patent 6645885). The patent proposes the creation of three-dimensional quantum-sized inclusions, the so-called "quantum dots", indium nitride (InN) and indium gallium nitride (InGaN) by organometallic gas-phase epitaxy. Moreover, the quantum dots of indium nitride (InN), indium gallium nitride (InGaN) are placed in quantum wells (QW) In _x Ga _1-x N / In _y Ga _1-y N. This technology allows you to create active layers of blue and green LEDs ranges, however, it is not possible to produce a white LED, since it covers a wavelength range from 480 to 530 nm. To obtain white light, it is necessary to have a wider spectrum of radiation from 400 to 750 nm.

The design and manufacturing technology of a white LED (third option of the third method) based on nitrides of elements of group III are described in patent RU2392695 C1 S.J. Chua (SJ Chua) et al. A white LED contains a n-type semiconductor layer, one or more structures with quantum wells formed on top of an n-type semiconductor, a p-type semiconductor layer formed on a structure with quart wells, a first electrode, formed on a p-type semiconductor, and a second electrode formed on a part of the n-type semiconductor layer. Each quantum well structure includes an In _x Ga _1-x N quantum well layer, an In _y Ga _1-y N barrier layer (x> 0.3 or x = 0.3), and In _z Ga _1-z quantum dots N, where x <y <z <l. The invention proposed two options for LEDs and two options for structures with quantum wells. This invention allows to create white LEDs that are easy to manufacture, have high light output and color rendering characteristics. An LED emits light in the range of about 400 to 750 nm. The molar fraction of the InN layer of the well, x, is important for expanding the emission range of the LED to the region of longer waves. At a higher x value in the In _x Ga _1-x N quantum well layer, the radiation wavelength extends to longer waves. If the value of x is equal to or greater than 0.3, the range of the emission spectrum of the structure with an MQW extends to 600 nm or more.

Thus, all the proposed methods for the manufacture of white LEDs are based primarily on the use of semiconductor crystals of nitrides of group III elements, either with the application of a phosphor to convert radiation, or without applying a phosphor, or involve the use of several LEDs in one housing.

Disclosure of invention

The problem solved by the present invention is the creation of a monolithic LED that emits from a single crystal the entire range of radiation of the visible part of the spectrum, in the range from 400 to 750 nm, at least, and can be made on the basis of a material different from nitrides of elements of group III, and without applying a phosphor. The technical result that allows us to accomplish this task is to increase the efficiency of using lateral radiation of p-n junction crystals and creating on this basis LEDs with an increased light flux and increased radiation power.

The technical result is achieved due to the fact that the white LED contains an η-type semiconductor layer formed from a GaP _1-xy As _x N _y semiconductor solid solution (0.3>x> 0, 0.030>y> 0.004), a heterostructure with its own type of conductivity formed from layers of GaP _1-xy As _x N _y semiconductor solid solutions (0.3>x> 0, 0.030>y> 0.004), formed over an n-type semiconductor layer, GaP _1-xy As _x N _y semiconductor layer (0.3> x > 0, 0.030>y> 0.004) p-type formed on the GaP _1-xy As _x N _y heterostructure (0.3>x> 0, 0.030>y> 0.004) with its own type of conductivity, the final tone p-type metamorphic layer of InGaAs semiconductor, where the molar fractions of nitrogen, y, and arsenic, x, smoothly or sharply change, simultaneously or separately, in the ranges 0.3>x> 0 and 0.030>y> 0.004, thereby forming a graded-gap semiconductor material. A heterostructure with its own type of conductivity, formed from layers of GaP _1-xy As _x N _y semiconductor solid solutions (0.3>x> 0, 0.030>y> 0.004), may not contain quantum wells or contain one or more quantum wells. In the case of the content of one or more quantum wells, the molar fractions of nitrogen, y, and arsenic, x, in the layers of quantum wells exceed the values of the molar fractions of nitrogen, y, and arsenic, x, in the layers of the quantum barrier, simultaneously or separately. In this case, the thickness of the GaP _1-xy As _x N _y quantum well layer is from 5 to 15 nm, and the In _y Ga _1-y N quantum barrier layer thickness is from 5 to 30 nm. An n-type semiconductor layer may be formed on the substrate, and this substrate may be made of GaP or Si. At least one of the elements of Si or Be can be used as dopants during molecular beam epitaxy growth.

The electroluminescence spectrum of a white LED is a continuous emission spectrum in the range from 400 to 1050 nm. To improve ohmic contact, a thin metamorphic layer of the InGaAs semiconductor, which is partially removed after the formation of metal electrodes, can be used as the final layer.

The present invention also provides a white light emitting diode heterostructure comprising an n-type semiconductor layer formed from GaP _1-xy As _x N _y semiconductor solid solutions (0.3>x> 0, 0.030>y> 0.004), a native type heterostructure conductivity formed from semiconductor layers of GaP _1-xy As _x N _y solid solutions (0.3>x> 0, 0.030>y> 0.004) formed over an n-type semiconductor layer, GaP _1-xy As _x N _y semiconductor layer >x> 0, 0.030>y> 0.004) a p-type formed on the GaP _1-xy As _x N _y heterostructure (0.3>x> 0, 0.030>y> 0.004) with its own type areas where the molar fractions of nitrogen, y, and arsenic, x, smoothly or sharply change, simultaneously or separately, in the ranges 0.3>x> 0 and 0.030>y> 0.004, thereby forming a graded-gap semiconductor material.

A heterostructure with its own type of conductivity formed from layers of GaP _1-xy As _x N _y semiconductor solid solutions (0.3>x> 0, 0.030>y> 0.004) may not contain quantum wells or contain one or more quantum wells. In the case of containing one or more quantum wells, the molar fractions of nitrogen, y, and arsenic, x, in the layers of quantum wells exceed the molar fractions of nitrogen, y, and arsenic, x, in the layers of the quantum barrier, simultaneously or separately. In this case, the thickness of the GaP _1-xy As _x N _y quantum well layer is from 5 to 15 nm, and the In _y Ga _1-y N quantum barrier layer thickness is from 5 to 30 nm. An n-type semiconductor layer may be formed on the substrate, and this substrate may be made of GaP or Si. At least one of the elements of Si or Be can be used as dopants during molecular beam epitaxy growth. To improve ohmic contact, a thin metamorphic layer of the InGaAs semiconductor, which is partially removed after the formation of metal electrodes, can be used as the final layer.

Semiconductor solid solutions with mixed anions, such as GaN _x As _1-x and GaN _x P _1-x, were introduced into a number of classical semiconductors by studies begun in the 60s of the twentieth century [DG Thomas, JJ Hopfield, and C.J . Frosch, Phys. Rev. Lett. 15, 857 (1965)]. The level of technological development of that time made it possible to realize GaN _x As _1-x and GaN _x P _1-x solid solutions with only a low nitrogen content (with a nitrogen concentration at the level of the dopant). Subsequent development of the technology for the synthesis of semiconductor compounds, synthesis methods such as molecular beam epitaxy (MPE) and gas phase epitaxy (HFE), allowed us to obtain solid solutions with a significantly higher nitrogen content (late 90s). Single-crystal layers of GaN _x As _1-x and GaN _x P _1-x with a nitrogen content of several percent damage were synthesized [A.Yu. Egorov, E.S. Semenova, V.M. Ustinov, YG Hong, S. Tu, FTP, vol. 36 (9), 1056-1059 (2002); H.Ch. Alt, A.Yu. Egorov, Η. Riechert, W. Wiedemann, JD Meyer, Physica B, v. 308-310, 877-880 (2001)], which can be considered as real ternary solid solutions with mixed anions, in contrast to previously synthesized binary compounds with isovalent doping. From that moment, intensive research began on this new class of semiconductor materials. It was found that the introduction of nitrogen fundamentally changes the properties of the new material. It turned out to be significant here that the electronegativity of nitrogen is significantly higher than the electronegativity of arsenic or phosphorus. The introduction of nitrogen, even at the level of one percent, leads to a complete modification of the electronic structure of the formed solid solution. Substitution of a small fraction of the elements of the fifth group, As and P, by N atoms in such solutions significantly modifies the conduction band, leads to its splitting and the formation of two nonparabolic subbands (E ^- and E ⁺ ). A model describing the formation of a new zone structure was proposed by Kent, Zunger et al. [PRС. Kent and Alex Zunger, Phys. Rev. B, v. 64, 115208 (2001); W. Shan, W. Walukiewicz, JW Ager III, Ε. E. Haller, JF Geisz, DJ Friedman, JM Olson, SR Kurtz, Phys. Rev. Lett., 82 (6), 1221 (1999); C. Skierbiszewski, P. Perlin, P. Wisniewski, W. Knap, T. Suski, W. Walukiewicz, W. Shan, KM Yu, JW Ager, EE Haller, JF Geisz, JM Olson. Appl. Phys. Lett., 76 (17), 2409 (2000); W. Shan, W. Walukiewicz, KM Yu, J. Wu, JW Ager, EE Haller, HP Xin, CW Tu. Appl. Phys. Lett., 76 (22), 3251 (2000)]. The proposed model made it possible to explain the unusual compositional dependence of the band gap, i.e., a decrease in the band gap of the solid solution with a decrease in the crystal lattice constant and a change in the fundamental properties of semiconductor materials, namely, the transition from the indirect structure of GaP energy bands to the direct-gap structure of the GaN _x P ₁ triple solid _-x at nitrogen concentrations, x, less than one percent.

So, the magnitude of the splitting of the subbands of the conduction band, E ^- and E ⁺ , in a quaternary GaP ₀ solid solution. _{74 of the} order of 1.11 eV. That is, it is practically possible to realize a multi-band semiconductor with two conduction bands, with a band structure that provides three optical transitions, approximately: 1.11 eV (1117 nm) between the E ^- and E ⁺ subbands, 1.67 eV (741 nm) between the ceiling of the valence band and the E subband ^- and 2.79 eV (445 nm) between the ceiling of the valence band and the E ⁺ subband. Such a set of transitions, when using this material as a light-emitting (active region) LED, allows one to receive radiation in an unusually wide spectral range, from 400 to 1050 nm. The electroluminescence spectrum of LEDs based on GaPAsN solid solutions covers almost the entire visible wavelength range and part of the near infrared range (Fig. 3).

When growing such solid solutions on gallium, GaP, and silicon, Si substrates, it is possible to achieve a fairly close lattice matching between the material of the epitaxial layer and the substrate material. Based on the Vegard law, the following ternary solid solutions with a zinc blende structure will be lattice-matched with Si and close to GaP at room temperature: GaN _y P _1-y (y = 0.02), GaN _y As _1-y (y = 0.19), InN _y P _1-y (y = 0.47), InN _y As _1-y (y = 0.56). Any linear combinations of these ternary solid solutions are also matched by the lattice parameter with the Si substrate and are close to GaP.

Currently, solid solutions of nitride-arsenides and nitride-phosphides with a molar fraction of nitrogen at the level of units of percent are practically realized, but, unfortunately, a further increase in the concentration of nitrogen leads to the destruction of the crystal structure of the epitaxial layer. However, an undoubted success is the fact that the introduction of such small fractions of nitrogen makes it possible to realize a practically significant range of solid solutions lattice-matched to standard substrates and to realize light-emitting devices based on them.

Signs and advantages of the invention can be achieved through the implementation of heterostructures indicated in the description and claims, as well as in the accompanying drawings.

Brief Description of the Drawings

FIG. 1 - Schemes of embodiments of LED heterostructures and white LEDs based on semiconductor GaPAsN solid solutions on GaP and Si substrates in accordance with the present invention;

FIG. 2 is a diagram of a white LED based on semiconductor GaPAsN solid solutions on a GaP substrate, with a deep mesa formed by etching, metal electrodes formed of gold, and a partially removed InGaAs final layer, in accordance with the present invention (arrows show the radiation coming up ( 1), from the ends (2) and down (3) through the substrate);

FIG. 3 - Electroluminescence spectrum at room temperature, with integrated registration of radiation in directions 1 and 2, white LEDs based on GaPAsN semiconductor solid solutions on a GaP substrate, with a deep round mesa 400 microns in diameter, formed by etching, metal electrodes formed of gold, in in accordance with the present invention (the lower spectrum is recorded at a voltage applied to the LED, 5 V; subsequent spectra are recorded with increasing voltage up to 14 V, in steps of 1, the upper spectrum is registered at a voltage of 18 V);

FIG. 4 - Electroluminescence spectrum at room temperature of a white LED based on semiconductor GaPAsN solid solutions on a GaP substrate, with a deep round mesa and metal electrodes formed of gold in accordance with the present invention, when radiation is recorded in direction 3 (part of the spectrum is “cut off” by due to the absorption of part of the radiation spectrum when passing through a GaP substrate).

The implementation of the invention

For growing layers of GaPAsN solid solutions, the MPE and HFE methods can be used. For the growth of heterostructures that are the subject of the present invention, the electroluminescence spectra of which are shown in FIG. 3 and FIG. 4, the molecular beam epitaxy (MBE) method was used with solid-state sources of gallium, phosphorus, and arsenic. To create a flow of atomic nitrogen to the epitaxial surface, a nitrogen source with a radio-frequency gas discharge was used. To create layers with n-type conductivity, doping with silicon, Si was used, and to create layers with p-type conductivity, doping with beryllium, Be was used. As a substrate for growing epitaxial heterostructures, GaP plates with a (100) surface orientation were used, but Si plates with an orientation close to (100) can also be used. In the case of using a GaP substrate, the heterostructure of the LED is formed on the surface of the GaP buffer layer, in the case of using a Si substrate, it is formed on the surface of the GaPN buffer layer, which is preceded by a thin germinal GaP layer. Typical epitaxy temperatures range from 490-580 degrees Celsius.

After growing the heterostructure of the LED by photolithography, liquid (or dry) etching, and vacuum deposition, deep mesa structures (etching depth exceeds the total thickness of all epitaxial layers) of round or rectangular shape and metal electrodes are formed.

Claims (15)

1. A white LED containing an n-type semiconductor layer formed from a GaP _1-xy As _x N _y semiconductor solid solution (0.3>x> 0, 0.030>y> 0.004), a heterostructure with its own type of conductivity, formed from semiconductor layers GaP _1-xy As _x N _y solid solutions (0.3>x> 0, 0.030>y> 0.004), formed over an n-type semiconductor layer, GaP _1-xy As _x N _y semiconductor layer (0.3>x> 0, 0.030 >y> 0.004) p-type, formed on the GaP _1-xy As _x N _y heterostructure (0.3>x> 0, 0.030>y> 0.004) with its own type of conductivity, completing a thin metamorphic layer of the p-type InGaAs semiconductor, g de the molar fractions of nitrogen, y, and arsenic, x, smoothly or sharply change, simultaneously or separately, in the ranges 0.3>x> 0 and 0.030>y> 0.004, thereby forming a graded-gap semiconductor material. 2. The white LED according to claim 1, characterized in that the heterostructure with its own type of conductivity, formed from layers of GaP _1-xy As _x N _y semiconductor solid solutions (0.3>x> 0, 0.030>y> 0.004), does not contain quantum pits. 3. The white LED according to claim 1, characterized in that the heterostructure with its own type of conductivity from the layers of GaP _1-xy As _x N _y solid solutions (0.3>x> 0, 0.030>y> 0.004) contains one or more quantum wells , and the values of the molar fractions of nitrogen, y, and arsenic, x, in the layers of quantum wells exceed the values of the molar fractions of nitrogen, y, and arsenic, x, in the layers of the quantum barrier, simultaneously or separately. 4. The white LED according to claim 3, characterized in that the thickness of the GaP _1-xy As _x N _y quantum well layer is from 5 to 15 nm, and the In _y Ga _1-y N quantum barrier layer thickness is from 5 to 30 nm 5. The white LED according to claim 1, characterized in that the n-type semiconductor layer is formed on the substrate, and this substrate is made of GaP or Si. 6. The white light emitting diode according to claim 1, wherein at least one of the elements Si or Be is used as dopants during the molecular beam epitaxy growth. 7. The white LED according to claim 1, characterized in that the electroluminescence spectrum is a continuous emission spectrum in the range from 400 to 1050 nm. 8. The white LED according to claim 1, in which to improve the ohmic contact, a thin metamorphic layer of the InGaAs semiconductor is used as the final layer, which is partially removed after the formation of metal electrodes. 9. LED heterostructure emitting white light, containing an η-type semiconductor layer formed from GaP _1-xy As _x N _y semiconductor solid solutions (0.3>x> 0, 0.030>y> 0.004), an intrinsic type heterostructure formed from semiconductor layers of GaP _1-xy As _x N _y solid solutions (0.3>x> 0, 0.030>y> 0.004) formed over an n-type semiconductor layer, a GaP _1-xy As _x N _y semiconductor layer (0.3>x> 0, 0.030>y> 0.004) p-type formed on the GaP _1-xy As _x N _y heterostructure (0.3>x> 0, 0.030>y> 0.004) with its own type of conductivity; the molar fractions of nitrogen, y, and arsenic, x, smoothly or sharply change, simultaneously or separately, in the ranges 0.3>x> 0 and 0.030>y> 0.004, thereby forming a graded-gap semiconductor material. 10. The LED heterostructure according to claim 9, characterized in that the heterostructure with its own type of conductivity, formed from layers of semiconductor solid solutions GaP _1-xy As _x N _y (0.3>x> 0, 0.030>y> 0.004), does not contain quantum pits. 11. The LED heterostructure according to claim 9, characterized in that the heterostructure with its own type of conductivity from the layers of GaP _1-xy As _x N _y solid solutions (0.3>x> 0, 0.030>y> 0.004) contains one or more quantum wells, and the molar fractions of nitrogen, y, and arsenic, x, in the layers of quantum wells exceed the molar fractions of nitrogen, y, and arsenic, x, in the layers of the quantum barrier, simultaneously or separately. 12. The LED heterostructure according to claim 11, characterized in that the thickness of the GaP _1-xy As _x N _y quantum well layer is from 5 to 15 nm, and the In _y Ga _1-y N quantum barrier layer thickness is from 5 to 30 nm . 13. The LED heterostructure according to claim 9, characterized in that the n-type semiconductor layer is formed on the substrate, and this substrate is made of GaP or Si. 14. The LED heterostructure according to claim 9, characterized in that at least one of the elements Si or Be is used as dopants during the molecular beam epitaxy growth. 15. The LED heterostructure according to claim 9, characterized in that to improve the ohmic contact, a thin metamorphic layer of the InGaAs semiconductor is used as the final layer, which is partially removed after the formation of metal electrodes.

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