RU1632278C - Method for manufacturing light-emitting diode patterns - Google Patents

Abstract

FIELD: semiconductor engineering. SUBSTANCE: p-n-p junction is shaped on SIC substrate by epitaxy; first SIC layer of p-type conductivity is applied, then that of n-type conductivity. After that substrate is irradiated by electrons; irradiation conditions are chosen so as to ensure homogeneous alloying of luminescent-active layer by radiation defects with predetermined and easily implemented concentration of centers of radiating recombination. For final procedure, pattern is annealed at 1700 to 1800 C. EFFECT: improved reproducibility of parameters.

Description

 The invention relates to semiconductor technology, in particular to the manufacture of light sources with radiation in green, blue and other spectral regions depending on the selected substrate polytype.

 The aim of the invention is to ensure reproducibility of the parameters of the structures.

 The proposed method allows you to first form a high-quality p-n junction by growing the p-type epitaxial layer on the n-type conductivity layer, and then, using electron irradiation and subsequent annealing, introduce luminescent-active centers into the n-layer. The need to build up the p-type conductivity layer on the n-type SiC layer is due to the fact that effective radiative recombination occurs in the p-type SiC layer in the case of injection of holes from the p-type SiC layer. The formed p-n junction should have the necessary physical parameters that ensure efficient uniform injection of holes into the luminescent active layer of the n-type conductivity.

 The need for electron irradiation of the created pn junction is due to the fact that this ensures almost uniform doping of the luminescent-active layer with radiation defects with a given and easily realized concentration of centers of radiative recombination, which leads to uniform luminescence over the area of the entire sample and reproducibility of the parameters of all LEDs, created on this sample.

 The energy of the irradiating electrons is in the range of 2.0-5.0 MeV. When irradiated with electrons with energies less than 2.0 MeV, an insufficient concentration of radiation centers of radiative recombination is formed and the luminescence efficiency decreases, i.e. LEDs degrade. When irradiated with electrons with an energy greater than 5.0 MeV, clusters are formed that can persist even after high-temperature annealing, which sharply affects the reproducibility of the LED parameters.

When irradiated with electrons in doses less than 10 ¹⁸ cm ^-2 , the concentration of luminescent-active radiation centers is significantly reduced, which leads to a decrease in the efficiency of electroluminescence and, consequently, to a deterioration in the parameters of LEDs. At a dose of electrons greater than 5 1810 ¹⁸ cm ^-2 , higher-temperature anneals are required to reduce the concentration of radiation nonradiative recombination centers. However, at temperatures above 1800 ^{° C} and annealing begins luminescence-active sites, which reduces the deterioration of luminescence efficiency and reproducibility of the parameters of LEDs.

Upon irradiation at a temperature below 30 ^{° C} reproducibility parameters LEDs decreases due to nonuniform distribution luminescence-active centers because of the low mobilities arising from radiation-induced defects. Irradiation at a temperature above 500 ^{° C} results in fewer centers radiative recombination due to the fact that the resulting radiation defects as set by positron spectroscopy, at such temperatures the irradiation combined into more complex systems, which are nonradiative recombination centers, which results in deterioration parameters LEDs.

At annealing temperatures below ^about 1700 C has not produced a sufficient amount of radiation-induced luminescence-active centers and are not fully annealed nonradiative recombination centers, which leads to deterioration of the LED parameters. At an annealing temperature higher than 1800 ^о С, annealing of the luminescent-active centers themselves begins, i.e. the luminescence efficiency decreases and the reproduction of the LED parameters deteriorates.

Example 1. As a substrate, SiC crystals of the 6H polytype of n-type conductivity with a concentration of uncompensated donors (Nd-Na) = 4 x 10 ¹⁸ cm ^-3 , determined by optical absorption, are used. The density of dislocations emerging on the basal plane (0001), not more than 10 ³ cm ^-2 . Etching in KOH at a temperature of 400 ^{° C} for 15 min removed from the surface of the substrate layer was 20 microns thick. After etching, polar faces (0001) were identified. Epitaxial layers are formed on the (0001) C plane, which is preferable from the point of view of creating mesa structures. Epitaxial buildup of n- and p-type conductivity layers is carried out by sublimation. The growth of the layers n-type conductivity is carried out in a vacuum of 10 ^-3 Pa, at a temperature of 1750 ^C for 1 hour. The samples were then monitored over the layer thickness and the concentration (Nd-Na). The layer thickness is measured on the prepared end sections using an MDL microscope with an accuracy of 1 μm and it is 15 μm. The concentration of (Nd-Na) is determined by the method of local breakdown of surface diodes and is 4˙10 ¹⁷ cm ^-3 . The growth of the p-type conduction layer is carried out in an Ar atmosphere in the presence of Al vapor (≈ 100 Pa) at a temperature of 2500 ^о С. The thickness of the extended layer is 5 μm. On the obtained structures, the concentration of Al acceptor impurity is measured, which was at a level of 5 × ^{20 20} cm ^-3 .

After the formation of the pn junction, the sample is irradiated with a stream of electrons at a linear accelerator. The irradiation dose of 10 ¹⁸ cm ^-2, the electron energy of 2.0 MeV irradiation temperature ^of 30 C. The obtained structure is annealed in argon at 1700 ^{° C} for 10 min.

 Then, to measure the electroluminescence parameters, ohmic contacts are formed: metal Al to the p-layer and alloy (Ni + W) to the n-layer.

Then, photolithography and etching in KOH create isolated LED structures (up to 200 structures on a single crystal) and measure the electroluminescence spectrum and the external quantum yield of the diode structure. Relative measurements of the quantum yield on all structures are carried out using a photometric head for measuring integrated power with a reference photocell. The maximum radiation lies in the spectral region of 530 nm. The external quantum yield was 2.0˙10 ^-4 with a spread across all structures of no more than 10%, which fully ensures the reproducibility of the parameters of the LEDs located on the same substrate and expands the scope of their use.

PRI me R 2. The conditions for the preparation of substrates, the modes of growth of the p-layers, the sequence of operations are the same as in example 1. The dose of irradiation with electrons 2.5 ˙ 10 ¹⁸ , the energy of 3.5 MeV, the irradiation temperature of 300 ^about annealing temperature 1750 ^о С, annealing time 10 min. An external quantum yield of 2.5 × 10 ^-4 with a spread across all structures of not more than 10%, which ensures reproducibility of the LED parameters on one substrate and expands the scope of their use.

PRI me R 3. The conditions for the preparation of substrates, the modes of growth of the pn layers, the sequence of operations are the same as in example 1. The dose of irradiation with electrons 5˙10 ¹⁸ cm ^-2 , the electron energy 5 MeV, the irradiation temperature 500 ^about C, annealing temperature 1800 ^о С, annealing time 10 min. An external quantum yield of 2.3˙10 ^-4 , with a spread across all structures of no more than 10%, which ensures reproducibility of the LED parameters on one substrate and expands the scope of their use.

PRI me R 4. The conditions for the preparation of substrates, the modes of growth of the pn layers, the sequence of operations are the same as in example 1. The radiation dose of 5-10 ¹⁷ cm ^-2 , energy 1.4 MeV, the irradiation temperature of 0 ^about C, the annealing temperature ^of 1650 C, the annealing time of 10 min. The quantum output of LEDs is 8˙10 ^-5 , with a spread across all structures of at least 30%.

PRI me R 5. The conditions for the preparation of substrates, the modes of growth of the pn layers, the sequence of operations are the same as in example 1. The dose of electron irradiation 10 ¹⁹ cm ^-2 , the electron energy of 6 MeV, the irradiation temperature of 600 ^about With annealing temperature 1850 ^{° C,} the annealing time of 10 min. The quantum output of LEDs is 10 ^-4 , with a spread across all structures of at least 30%.

 As can be seen from examples 4 and 5, where the transcendental parameters of irradiation with electrodes and annealing of structures are given, the positive effect is sharply reduced.

PRI me R 6. As the substrate using crystals of SiC polytype 4H n-type conductivity with a concentration of uncompensated donors (Nd - Na) = 4 × ^{18 18} cm ^-3 . Conditions of preparation of substrates capacity modes p-n-layers, the sequence of operations are the same as in Example 1. The electron irradiation dose 2,5˙10 ^18, the energy of 3.5 MeV, the irradiation temperature is ^about 300 C, the annealing temperature 1750 ^{° C,} annealing time 10 min.

The maximum emission of LED structures lies in the spectral region 4850A. The external quantum yield was 1˙10 ^-4 with a spread across all structures of no more than 10%, which fully ensures the reproducibility of the parameters of the LEDs located on the same substrate and expands the field of their use.

 Thus, the proposed method for manufacturing the LED provides reproducibility of the parameters of the LEDs created on the same substrate and expands the scope of their use (for example, to create modules for recording and reproducing information in analog modes).

 Simplification and optimization of the technology can be considered additional advantages, since there is no danger of thin p-layer evaporation and the LEDs obtained by the proposed method have high speed (response time τ время 10 ns), which ensures high recording and reproduction density of information in optoelectronic systems.

Claims (1)

METHOD FOR PRODUCING LED STRUCTURES by epitaxial growth of an n-type SiC layer on a SiC substrate, an n-type conductivity SiC layer, an p-type SiC layer on a p-type SiC layer, irradiation and annealing, characterized in that, in order to ensure reproducibility of the parameters, the irradiation is carried out by electrons with energy of 2 - 5 MeV with a dose of 10 ¹⁸ - 5 · 10 ¹⁸ cm ^-2 at a temperature of 30 - 500 ^o C, and annealing is carried out at a temperature of 1700 - 1800 ^o C.