RU2262156C1 - Semiconductor element emitting light in ultraviolet range - Google Patents

Abstract

FIELD: semiconductor emitting devices.

SUBSTANCE: proposed semiconductor element that can be used in light-emitting diodes built around broadband nitride elements of A^IIIB^V type and is characterized in ultraviolet emission range extended to 240 -300 nm has structure incorporating substrate, buffer layer made of nitride material, n contact layer made of Si doped nitride material Al_XIIn_X2Ga_I-XI-X2N, active layer made of nitride material Al_VIIn_Y2Ga_I-YI-Y2N, and p contact layer made of Mg doped nitride material Al_ZIIn_Z2Ga_I-ZI-Z2N; active layer is divided into two areas; area abutting against contact layer is doped with Si and has n polarity of conductivity; other area of active layer is doped with Mg and has p polarity of conductivity; molar fraction of Al (YI) in p area of active layer is continuously and monotonously reducing between its boundary with n contact layer and boundary with p area of contact layer and is within the range of 0.1 ≤ VI ≤ 1; difference in VI values at boundaries of active-layer n area is minimum 0.04 and width of forbidden gap in active-layer p area at its boundary with active-layer n area exceeds by minimum 0.1 eV the maximal width of n area forbidden gap.

EFFECT: enlarged ultraviolet emission range, enhanced inherent emissive efficiency, simplified design of light-emitting component.

1 cl, 1 dwg, 1 tbl

Description

The invention relates to the field of semiconductor emitting devices, and more particularly to LEDs based on wide-gap nitride compounds of type A ^III B ^V.

Known semiconductor light-emitting element containing a substrate, a buffer layer, an n-contact layer made of GaN and doped with Si, a p-contact layer made of GaN and doped with Mg, F. Calle et al., MRS J. Nitride Semicond. Res. 3 (1998) 24.

This technical solution provides the maximum simplicity of the design of the device, but does not allow to obtain high internal radiation efficiency and a radiation wavelength of less than 365 nm.

Also known is a semiconductor element emitting light in the ultraviolet range, the structure of which consistently includes a substrate, a buffer layer made of nitride material, an n-contact layer made of nitride material Al _x1 In _y1 Ga _1-x1-y1 N, doped with Si, active a layer made of nitride material Al _x2 In _y2 Ga _1-x2-y2 N, simultaneously doped with donors and acceptors, and a p-contact layer made of nitride material Al _x3 In _y3 Ga _1-x3-y3 N, doped with Mg, where the above layers form either one-sided, l bo bi-heterostructure, US 6,005,258.

In this design, to increase the internal quantum efficiency of the light-emitting element, either the active layer of the heterostructure is donated and accepted by the donors and acceptors, or the one-sided structure is replaced by a two-sided one.

This technical solution is selected as a prototype of the present invention.

However, this semiconductor light emitting element is suitable primarily for generating radiation with a wavelength of 350 nm or more. In the shorter wavelength range, the internal radiation efficiency of the prototype device is sharply degraded.

This is explained by the fact that for the element to operate in the ultraviolet spectral range (with a radiation wavelength of 300 nm or less), the use of nitride compounds with a high AlN content is required. In this case, the most significant factors determining the radiation efficiency are carrier limitation in the active layer and suppression of potential barriers associated with polarization charges arising at interfaces with an abrupt change in composition. In the prototype device, limiting the media within the active layer is not enough. As a result, injected holes can freely penetrate into the n-contact layer, and electrons can penetrate into the p-contact layer, where they recombine predominantly nonradiatively, leading to a sharp decrease in the internal efficiency.

The basis of this invention is the solution to the problem of expanding the range of ultraviolet radiation to 240-300 nm, increasing the internal radiation efficiency while simplifying the design of the light-emitting element.

According to the invention, this problem is solved due to the fact that in the semiconductor element emitting light in the ultraviolet range, the structure of which consistently includes a substrate, a buffer layer made of nitride material, an n-contact layer made of nitride material Al _X1 In _X2 Ga _{1- X1-X2} N doped with Si, an active layer made of nitride material Al _Y1 In _Y2 Ga _1-Y1-Y2 N, and a p-contact layer made of nitride material Al _Z1 In _Z2 Ga _1-Z1-Z2 N doped Mg, the active layer is divided into two regions, while the adjacent the contact layer, the region is doped with Si and has n-type conductivity, and the other region of the active layer is doped with Mg and has p-type conductivity, the molar fraction of Al (Y1) in the region of the active layer with n-type conductivity continuously and monotonously decreases from the boundary with n- contact layer to the boundary with the region of the active layer having p-type conductivity, and is in the range 0.1≤Y1≤1, and the difference in the values of Y1 at the boundaries of the region of the active layer with n-type conductivity is at least 0.04, and the width band gap in the region of the active layer with conductivity p-type at its boundary with the region with n-type conductivity is not less than 0.1 eV exceeds the maximum band gap of the region with n-type conductivity.

The applicant has not identified sources containing information about technical solutions identical to the present invention, which allows us to conclude that it meets the criterion of "novelty."

The implementation of the distinguishing features of the invention provides an increase in the radiation efficiency due to the expansion of the active layer in comparison with traditional double-sided structures based on quantum wells, where the quality of interfaces and the doping profile near them are a critical factor. In addition, the wide active region reduces the heat load on the active layer, which further contributes to an increase in the efficiency of the device.

The use of the InN content in heterostructure layers with the indicated molar fractions of In, on the one hand, helps to reduce the concentration of intrinsic point defects in the material, which is favorable for increasing the internal radiation efficiency, and, on the other hand, does not lead to decomposition into phases of Al _x In _y solid solutions Ga _1-xy N, accompanied by the generation of extended defects, sharply reducing the quantum yield of radiation.

To suppress the penetration of holes into the n-contact layer in the proposed design, a smooth change in the band gap in the n-region of the active layer is applied due to variations in its composition. This creates a built-in electric field for holes, pulling them away from the n-contact layer towards the boundary of the pn junction. The magnitude of the pulling field is controlled by the difference in the values of y at the boundaries of the region of the active layer with n-type conductivity within 0.04.

To prevent the penetration of electrons into the p-contact layer, a jump in the composition (and, consequently, the band gap) is formed at the boundary of the regions of the active layer with n- and p-type conductivity (n- and p-regions). For the potential electron barrier created by this jump to be effective even at high injection levels, it is necessary that the band gap in the p region of the active layer at its boundary with the n region be 0.1 eV larger than the maximum band gap in n -regions of the active layer.

The applicant has not found any sources of information containing information on the impact of the claimed distinctive features on the technical result achieved as a result of their implementation. This, according to the applicant, indicates that this technical solution meets the criterion of "inventive step".

The semiconductor element in a specific embodiment in all examples has a structure that includes in series:

- a substrate 1 made of sapphire with a thickness of 500 μm;

- buffer layer 2 of AlN with a thickness of 20 nm;

- n-contact layer 3 made of AL _X1 IN _X2 GA _1-X1-X2 N, in this example, X ₁ = 0.52; X ₁ may vary from 0.1 to 1.0; X ₂ can vary from 0 to 0.05. Layer 3 is doped with silicon with a concentration of 5 · 10 ¹⁸ cm ^-3 , a thickness of 1.5 microns;

- the active layer made of Al _Y1 In _Y2 Ga _1-Y1-Y2 N, where Y ₁ = 0.52, can lie in the range from 0.1 to 1, Y ₂ = 0 and can be in the range from 0 to 0 , 05; the active layer includes region 4 doped with Si with a concentration of 5 · 10 ¹⁸ cm ^-3 with n-type conductivity and region 5 doped with Mg with a concentration of 5 · 10 ¹⁹ cm ^-3 having p-type conductivity;

- p-contact layer 6 made of Al _Z1 In _Z2 Ga _1-Z1-Z2 N, in which the value of Z ₁ = 0.52; Z ₁ may vary from 0.1 to 1.0; Z ₂ may be in the range from 0 to 0.05. Layer G is doped with magnesium with a concentration of 5 · 10 ¹⁹ cm ^-3 and a thickness of 100 nm.

The semiconductor element is a one-sided LED heterostructure with a variable composition of the active layer, which allows one to obtain an internal efficiency of 15-35% at current densities varying from 1 A / cm ² to 100 A / cm ² and the density of penetrating dislocations is ~ 10 ⁹ cm ^-2 . It should be noted that a decrease in the dislocation density in an LED leads to a sharp increase in its internal efficiency. With a dislocation density of ~ 10 ⁷ cm ^-2, it is possible to obtain an internal quantum yield in excess of 90%.

For testing, heterostructures were grown on a sapphire substrate by MOS hydride epitaxy at subatmospheric pressure and temperatures from 1000 ° C to 1100 ° C, n-contact layers and n-regions of active layers were doped with Si to a concentration of 5 · 10 ¹⁸ cm ^-3 , which was established using SIMS (secondary ion mass spectrometry). p-regions of the active layers and p-contact layers were doped with Mg to a concentration of 5 · 10 ¹⁹ cm ^-3 .

After the growth process, the structure was subjected to dry (ion) etching in order to form a mesa to a depth corresponding to the level of the n-contact layer. Then, the n and p contacts, which are multilayer metal compositions, respectively, Ti / Al / Pt / Au and Ni / Au, were applied to the etched and remaining parts of the structure, respectively. The contacts were burned in an atmosphere of nitrogen at a temperature of 850 ° C for 30 seconds.

Further, individual LEDs were cut out from the structure, which were mounted on the heat sink with the p-contact down, and gold electrodes were soldered to them to supply electric current.

To study the luminescent characteristics of LEDs, we used a KSVU-12 spectrometer with a specially selected diffraction grating, which allows measurements in the ultraviolet spectral range. An FEU-100 photomultiplier was used as a detector. The signal from the photomultiplier was transmitted to a computer through the Sch1413 digital voltmeter for final processing of the measurement data.

The accuracy of radiation intensity measurements was no worse than 0.02%.

To measure the external efficiency of the LED, a calibrated photodetector based on amorphous Si: H (hydrogen doped silicon) was used. The measurements were carried out with a fixed experimental geometry, which made it possible to quantitatively compare the radiation of various samples.

The electroluminescence of LEDs was measured when radiation was output through a sapphire substrate.

The characteristics of semiconductor light-emitting elements obtained as a result of the tests are shown in Table 1.

Table 1 Example Number Semiconductor element parameters Internal quantum efficiency at a current density of 1 to 10 ² A / cm ² Wavelength range (nm) 1 The proportion of Al Y ₁ = 0.42 in the n-region (50 nm), and Y ₁ = 0.62 in the p-region (50 nm); Al fraction in the p-contact layer Z ₁ = 0.62 0.14-0.11 250-290 2 The proportion of Al Y ₁ = 0.42 in the n-region (50 nm), and Y ₁ = 0.70 (10 nm) near the boundary with the n-region and Y ₁ = 0.52; Al fraction in the p-contact layer Z ₁ = 0.52 0.13-0.14 250-290 3 The Al fraction decreases from Y ₁ = 0.52 to 0.42 at a thickness of 10 nm in the n-region, and then increases from Y ₁ = 0.42 to Y ₁ = 0.62 at a thickness of 10 nm in the p-region; Al fraction in the p-contact layer Z ₁ = 0.62 0.15-0.23 250-290 4 The Al fraction decreases from Y ₁ = 0.52 to 0.42 at a thickness of 20 nm in the n-region, and then increases from Y ₁ = 0.52 to Y ₁ = 0.70 at a thickness of 10 nm in the p-region; Al fraction in the p-contact layer Z ₁ = 0.52 0.17-0.32 250-290 5 The Al fraction decreases from Y ₁ = 0.52 to 0.42 at a thickness of 50 nm in the n-region, and then is Y ₁ = 0.62 at a thickness of 20 nm in the p-region; Al fraction in the p-contact layer Z ₁ = 0.62 0.15-0.34 250-290 6 The Al fraction decreases from Y ₁ = 0.52 to 0.42 at a thickness of 20 nm in the n-region, and then is Y ₁ = 0.62 at a thickness of 20 nm in the p-region; Al fraction in the p-contact layer Z ₁ = 0.62 0.17-0.22 250-290 7 The Al fraction decreases from Y ₁ = 0.62 to 0.52 at a thickness of 20 nm in the n-region, and then increases from Y ₁ = 0.42 to Y ₁ = 0.54 at a thickness of 50 nm in the p-region; Al fraction in the p-contact layer Z ₁ = 0.54 0.02-0.12 250-290

In examples 3, 4, 5, 6, the internal quantum efficiency of a semiconductor device exceeds 15% and reaches a level of more than 30% on individual structures at a current density of 100 A / cm ² . A further increase in current density leads to an increase in efficiency up to ~ 50% at a current density of ~ 1 kA / cm ² , which is important for creating high-power LEDs and ultraviolet lasers.

The above examples confirm the high radiation efficiency in the short-wave part of the ultraviolet spectrum.

To implement the light-emitting elements used standard industrial equipment, which determines the compliance of the invention with the criterion of "industrial applicability".

Claims (1)

A semiconductor element emitting light in the ultraviolet range, the structure of which consistently includes a substrate, a buffer layer made of nitride material, an n-contact layer made of nitride material Al _X1 In _X2 Ga _1-X1-X2 N, doped with Si, active layer, made of nitride material Al _Y1 In _Y2 Ga _1-Y1-Y2 N, and a p-contact layer made of nitride material Al _Z1 In _Z2 Ga _1-Z1-Z2 N doped with Mg, characterized in that the active layer is divided into two region, while the region adjacent to the contact layer is doped with Si and has n-type conductivity, and the other region of the active layer is doped with Mg and has p-type conductivity, the molar fraction of Al (Y ₁ ) in the region of the active layer with n-type conductivity continuously and monotonously decreases from the boundary with the n-contact layer to the boundary with the region of the active layer having p-type conductivity and is in the range 0.1≤Y ₁ ≤1, and the difference in the values of Y ₁ at the boundaries of the region of the active layer with n-type conductivity is at least 0.04, and the band gap is regions of the active layer with p-type conductivity at its boundary with the region with gence n-type is not less than 0.1 eV greater than the maximum band gap region with n-type conductivity.