RU2381596C1 - Light-emitting diode heterostructure - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: according to the invention, the light-emitting diode heterostructure based on solid solutions of nitrides of group three metals Al_xIn_yGa_1(x+y)N (0≤x≤1, 0≤y≤1) with a p-n junction has an n-contact layer made from nitride material GaN, an active region with quantum wells formed by layers made from nitride material In_yGa_1-yN, a depletion layer made from nitride material Al_xGa_1-xN, a p-contact layer made from nitride material GaN. The depletion layer has varying composition with respect to aluminium on its thickness. In the direction of epitaxial growth of the heterostructure after the n-contact layer there is depletion layer. After the depletion layer there is an active region, and after the active region there is a p-contact layer. The depletion layer has on its thickness a first zone in which aluminium content increases from zero to a maximum value corresponding to aluminium content of the depletion layer material, a second zone in which aluminium content remains constant, and a third zone in which aluminium content falls from maximum to zero.

EFFECT: invention minimises mechanical stress on the border of the depletion layer with respect to the light-emitting diode heterostructure, in which the depletion layer lies after the n-contact layer and in front of the active region.

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Description

The invention relates to the field of semiconductor light-emitting devices, in particular to LEDs based on solid solutions of metal nitrides of the third group.

Known LED heterostructures based on solid solutions of metal nitrides of the third group AlInGaN with a pn junction containing a sequence of epitaxial layers that traditionally include an n-contact layer made of GaN nitride material, an active region with quantum wells formed by layers made of nitride material In _y Ga _1-y N, a barrier layer made of nitride material Al _x Ga _1-x N, a p-contact layer made of nitride material GaN.

During the epitaxial growth of a heterostructure, defects in its crystal lattice may arise due to differences in the chemical composition of the material of its layers. During epitaxial growth, when passing from one layer to another, atoms of one element are replaced by atoms of another element or one of the elements is excluded from the composition of the material, which can cause mechanical stresses due to the difference in the constant crystal lattices. These stresses are the cause of various kinds of defects (point defects, dislocations, microcracks, etc.) in the LED heterostructure.

The above defects adversely affect the efficiency of light emission in the heterostructures under consideration. Moreover, to the greatest extent these characteristics are affected by defects arising in the active region in which radiative recombination of charge carriers occurs.

Known LED heterostructures based on solid solutions of metal nitrides of the third group AlInGaN [for example, RU 2262155, RU 2277736, JP 2001085735], in which the barrier layer is located after the active region in the direction of epitaxial growth, while to reduce mechanical stresses in the barrier layer, the aluminum content in it varies in the thickness of the layer.

As the closest analogue of the claimed technical solution, the authors chose a LED heterostructure based on solid solutions of metal nitrides of the third group Al _x In _y Ga _{1- (x + y)} N (0≤x≤1, 0≤y≤1) with pn junction described in JP 2001085735.

This heterostructure contains, in the direction of its epitaxial growth, an n-contact layer made of GaN nitride material, an active region with quantum wells formed by layers made of In _y Ga _1-y N nitride material, a barrier layer made of Al _x Ga nitride material _1-x N, p-contact layer made of GaN nitride material. The barrier layer located after the active region has a composition with respect to aluminum that is variable in thickness, namely, the aluminum content in the barrier layer decreases linearly from the maximum at the boundary with the active region to the minimum at the boundary with the p-contact layer.

In the heterostructure under consideration, at the boundary of the barrier layer, where it is in contact with the p-contact layer, there is no abrupt change in the composition of the material, which helps to reduce the probability of generation of defects in the barrier layer. However, since at the other boundary of the barrier layer, where it is in contact with the active region, the aluminum content abruptly changes from zero to maximum, in the heterostructure under consideration there is still a high probability of occurrence of defects, including defects in the crystal structure of the active region.

It should be noted that the presence of strong mechanical stresses at the boundary of the barrier layer is especially critical for heterostructures in which the active region is located after the barrier layer in the direction of their epitaxial growth, since the defects of the previous layer (layers) due to the presence of stresses largely determine the appearance of defects in the subsequent layer (layers).

The objective of the invention is to minimize mechanical stresses at the boundary of the barrier layer in relation to the LED heterostructure in which the barrier layer is located after the n-contact layer and in front of the active region.

The essence of the claimed invention lies in the fact that in the LED heterostructure based on solid solutions of metal nitrides of the third group Al _x In _y Ga _{1- (x + y} ) N (0≤x≤1, 0≤y≤1) with pn junction containing an n-contact layer made of GaN nitride material, an active region with quantum wells formed by layers made of In _y Ga _1-y N nitride material, a barrier layer made of Al _x Ga _1-x N nitride material, p -contact layer made of GaN nitride material, while the barrier layer has a variable composition in thickness with respect to aluminum, according to the invention, in the direction of epitaxial growth of the heterostructure after the n-contact layer there is a barrier layer, after the barrier layer there is an active region, and after the active region there is a p-contact layer, while the barrier layer has a thickness in thickness of the first zone in which the content aluminum increases from zero to a maximum value corresponding to the aluminum content in the composition of the material of the barrier layer, the second zone in which the aluminum content remains unchanged and the third zone, in which the aluminum content decreases from the maximum value to zero.

In the inventive LED heterostructure in which a barrier layer made of Al _x Ga _1-x N material is located after the n-contact layer and the active region is located after the barrier layer, the above-described three-zone is proposed to minimize the likelihood of crystal lattice defects at the boundaries of the barrier layer structure of the barrier layer. This structure of the barrier layer ensures the achievement of the aluminum content required in the composition of the material of the barrier layer, with the exception of the occurrence of spasmodic changes in the composition of the material at its boundaries, where the barrier layer is in contact with layers that do not contain aluminum.

This structure of the barrier layer was experimentally selected by the authors. As shown by the authors of the study, in the inventive heterostructure with the above-described three-zone barrier layer, the number of defects of the crystal lattice is significantly reduced, including in the active region. This is explained by the fact that with a gradual increase in the aluminum content in the composition of the barrier layer as it grows to the required value, keeping the achieved required content within a certain thickness of the barrier layer and a gradual decrease in the aluminum content in the specified layer to zero, better coordination of the constant crystal lattice of the barrier occurs and adjacent to it on both sides of the layers, not containing aluminum, thereby minimizing the likelihood of crystal defects lattice in the barrier layer and at its boundaries.

Thus, the technical result achieved by using the claimed invention is to minimize the concentration of crystal lattice defects in the barrier and overlying layers in relation to the LED heterostructure in which the barrier layer is located after the n-contact layer and in front of the active region.

Figure 1 presents a diagram of the inventive LED heterostructure; figure 2 presents a graphical dependence showing the nature of the change in the aluminum content along the thickness of the barrier layer.

The inventive LED heterostructure with a pn junction (see Fig. 1) sequentially in the direction of its epitaxial growth includes:

n-contact layer 1 made of nitride material (GaN) n-type conductivity, used for spreading current;

a barrier layer 2 made of nitride material (Al _x Ga _1-x N) n-type conductivity;

active region 3 with several quantum wells formed by layers made of unalloyed nitride material (In _y Ga _1-y N), separated by barriers made of nitride material (GaN);

p-contact layer 4 made of nitride material (GaN) p-type conductivity.

The indicated sequence of layers is used, for example, in one of the possible embodiments of the so-called inverse LED heterostructure based on solid solutions of metal nitrides of the third group Al _x In _y Ga _{1- (x + y)} N (0≤x≤1, 0≤y≤ 1) with the pn junction described, in particular, in RU 2306634 and presented in figure 1 of the description of the specified patent.

A fundamental feature of the inverse semiconductor light-emitting heterostructure is that the active region is located in the p-type region so that the carrier recombination intensity in the active region is determined not by hole injection, but by electron injection. An advantage of the considered inverse heterostructure is its high injection efficiency.

In an LED heterostructure (see FIG. 1), layers 1 and 2 form an n-type conductivity region, an active region 3 with quantum wells and barriers, and a p-contact layer 4 form a p-type conductivity region.

The upper arrows in figure 1 indicate the injection of electrons into the active region, the lower arrow indicates the injection of holes into the active region. The arrow below the figure indicates the direction of epitaxial growth of the heterostructure.

The barrier layer 2 (see FIG. 2) in the direction of its epitaxial growth contains three zones in thickness (X). In the first zone, the aluminum content increases from zero to a maximum value corresponding to the aluminum content in the composition of the considered layer. In particular, the aluminum content increases linearly from zero over the thickness of the first zone, in particular, 2-6 nm, to 10-20%. In the second zone, the aluminum content remains unchanged in its thickness, comprising, in particular, 20-40 nm. In the third zone, the aluminum content decreases linearly from the maximum value to zero in its thickness, which is, in particular, 1-5 nm.

The inventive LED heterostructure can be obtained by gas-phase epitaxy from organometallic compounds on a substrate, in particular, made of sapphire.

LED heterostructure works as follows.

When passing current in the forward direction, electrons from the n-type conduction region are injected into the active region located inside the p-type conduction region. Holes from the region of p-type conductivity also enter the active region. In this case, the barrier layer 2, located in the region of n-type conductivity, prevents the penetration of holes from the p-region into the n-region of conductivity.

Electrons and holes moving towards each other recombine, transferring their energy to light quanta. The recombination of charge carriers occurs in quantum wells of the active region, the material of which has a band gap that is smaller than the rest of the material of the active region.

Claims (1)

A semiconductor light-emitting heterostructure based on solid solutions of metal nitrides of the third group Al _x In _y Ga _{1- (x + y)} N (0≤x≤1, 0≤y≤1) with a pn junction containing an n-contact layer, made of GaN nitride material, an active region with quantum wells formed by layers made of In _y Ga _1-y N nitride material, a barrier layer made of Al _x Ga _1-x N nitride material, a p-contact layer made of nitride GaN material, while the barrier layer in thickness has a variable composition with respect to aluminum, different in that, in the direction of epitaxial growth of the heterostructure after the n-contact layer, the barrier layer is located, after the barrier layer there is an active region, and after the active region there is a p-contact layer, while the barrier layer in thickness contains the first zone in which the aluminum content increases from a zero value to a maximum value corresponding to the aluminum content in the composition of the material of the barrier layer, a second zone in which the aluminum content remains unchanged, and a third zone in which aluminum ue decreases from a maximum value to zero.

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