CN105957936B - A kind of DUV LED epitaxial wafer structure - Google Patents

Abstract

The invention belongs to field of optoelectronic devices, specifically a kind of DUV LED epitaxial wafer structure, including substrate, the substrate top surface to sequentially consist of cushion, n AlGaN layers, multi-quantum well luminescence layer, p AlGaN layers and p GaN contact layers；The multi-quantum well luminescence layer is made of some be alternately stacked from bottom to top successively to well layer and barrier layer, which is Al_xGa_1‑xN/Al_zIn_yGa_1‑y‑zN/Al_xGa_1‑xN, wherein the value of 0.6≤x≤0.9, y and z will meet E_g（Al_zIn_yGa_1‑y‑zN）<E_g（Al_xGa_1‑xN）, barrier layer AlN.Using in Al_xGa_1‑xInserted with Al in N well layer_zIn_yGa_1‑y‑zThe structure of N thin layers, to regulate and control the relative position that heavy hole band, light hole band, crystalline field cleave hole band, improves TE moulds light and reduces the ratio of TM mould light, so as to improve the luminous efficiency of DUV LED.

Description

A DUV LED epitaxial wafer structure

technical field

The invention belongs to the field of optoelectronic devices, in particular to a DUV LED epitaxial wafer structure.

Background technique

Ultraviolet light-emitting diodes (LEDs) have the advantages of environmental protection and non-toxicity, low power consumption, small size and long life, and meet the requirements of environmental protection and energy saving in the new era. The emission wavelength of AlGaN-based LEDs can cover the range of 210nm-360nm, of which 210nm-300nm belongs to the deep ultraviolet band. Deep ultraviolet LEDs have great application value in printing, medical treatment, purification, detection, data storage and lighting.

Compared with GaN-based blue LEDs, deep-UV LEDs with wavelengths shorter than 300nm generally have lower luminous efficiencies. As the light-emitting wavelength of AlGaN-based LEDs gradually shortens, the Al composition in the light-emitting layer AlGaN will increase accordingly, and the difficulty of material epitaxial growth, doping, and device fabrication will also increase, and the light output power will gradually decrease. On the one hand, when the Al composition is higher than 0.5, the crystal field splits the hole band to replace the heavy hole band and the light hole band to become the top of the valence band, so that the light emission from the front (TE mode) is quickly replaced by the light emission from the side (TM mode), which fundamentally limits the light extraction efficiency. On the other hand, with the increase of the Al composition, the activation energy of the donor/acceptor increases correspondingly, so that the activation rate of p-type doping is very low, and the hole concentration is very low at room temperature. When the Al composition is higher than 0.5, the hole concentration in p-AlGaN is too low to form a good ohmic contact with the electrode. In order to reduce the p-type ohmic contact resistance, a p-GaN cap layer needs to be introduced, but p-GaN will absorb photons and Reduce luminous efficiency. This is also the reason why the high Al composition AlGaN LED adopts a bottom-emitting flip-chip structure. However, traditional patterned substrates, surface roughening, anti-reflection layers, high-reflective mirrors and other technologies have limited effects on improving the light extraction efficiency of deep ultraviolet LEDs.

Contents of the invention

In order to improve the luminous efficiency of the DUV LED, the present invention provides a DUV LED epitaxial wafer structure.

The present invention is achieved through the following technical solutions: a DUV LED epitaxial wafer structure, including a substrate, the upper surface of the substrate is sequentially composed of a buffer layer, an n-AlGaN layer, a multi-quantum well light-emitting layer, and a p-AlGaN layer from bottom to top. Layer and p-GaN contact layer; the multi-quantum well light-emitting layer is composed of several pairs of well layers and barrier layers stacked alternately from bottom to top, and the well layer is Al _x Ga _1-x N/Al _z In _y Ga _1-yz N/Al _x Ga _1-x N, where 0.6≦x≦0.9, the values of y and z should satisfy E _g (Al _z In _y Ga _1-yz N)< E _g (Al _x Ga _{1- x} N), the barrier layer is AlN; the thickness of the Al _z In _y Ga _1-yz N layer in the well layer is 0.3-2nm, and the thickness of the well layer is smaller than the thickness of the barrier layer.

In the technical solution of the present invention, a structure in _which a thin layer of Al _{zInyGa1 -yzN is inserted in the AlxGa1-xN well layer} is used to control the heavy hole band, the light hole band, and the crystal field splitting hole The relative position of the band, the x value is mainly to regulate the emission wavelength, so that the target wavelength is in the deep ultraviolet range. If the thickness of the thin-layer structure is too large, the _{AlzInyGa1 -yzN} insertion layer will act as _a quantum well, causing the luminescence peak of the non-target wavelength to appear and the spectrum to broaden, while weakening the luminescence peak of the target wavelength. If the thickness is too small, it is difficult to control. And it doesn't work accordingly.

Preferably, the total thickness of the two _{AlxGa1 -} xN layers in the well layer is 2-5 nm, and the thickness of the barrier layer is 5-20 nm.

Further, the buffer layer is an AlN buffer layer, or a buffer layer composed of an AlN layer and an AlGaN/GaN superlattice.

Further, the number of periods of well layers and barrier layers in the multi-quantum well light-emitting layer is 1-20 pairs.

Further, the growth temperature of the Al _x Ga _1-x N layer is the same as the growth temperature of the Al _z In _y Ga _1-yz N layer in the preparation process of the multi-quantum well light-emitting layer, which simplifies the process and avoids the heating and cooling process.

The DUV LED epitaxial wafer structure described in the present invention adopts a structure in which a _thin layer of Al _{zInyGa1 -} yzN is inserted in the _{AlxGa1 -} xN well layer to control the heavy hole band and the light hole band , The relative position of the crystal field splitting hole band, increasing the TE mode light and reducing the proportion of TM mode light, thereby improving the luminous efficiency of DUV LED.

Description of drawings

Figure 1 is a schematic diagram of the structure of the DUV LED provided by the present invention (the substrate is sapphire). Of course, other substrate materials, such as Si, SiC, etc., may also be used in some embodiments.

Fig. 2 is a schematic diagram of the valence band of a general Al _0.8 Ga _0.2 N/AlN structure quantum well. As shown in the figure, the crystal field splitting hole band is located above the heavy hole band and the light hole band, which means that the light component generated by quantum well radiative recombination is mainly TM mode light, and only a small part of TE mode light, also That is to say, there is very little light emission perpendicular to the c-plane, which is not conducive to light extraction.

Figure 3 is a schematic diagram of the valence band of the _{AlxGa1 -xN / AlzInyGa1 -yzN} / _{AlxGa1 -xN} /AlN structure quantum well provided by Example 1 of the present invention, x=0.8, y =z=0.05. As shown in the figure, inserting a thin layer of Al _0.05 In _0.05 Ga _0.9 N into Al _0.8 Ga _0.2 N can adjust the energy band, so that the heavy hole band and the light hole band are located above the crystal field splitting band, which means that the quantum well The light component generated by radiative recombination is mainly TE mode light, that is, the light emission perpendicular to the c-plane is improved, which is beneficial to improve the luminous efficiency of the device.

Detailed ways

Example 1

A DUV LED epitaxial wafer structure, including a substrate, on which there are AlN buffer layer, n-AlGaN layer, multi-quantum well light-emitting layer, p-AlGaN layer and p-GaN contact layer from bottom to top; The multi-quantum well light-emitting layer is composed of a pair of well layers and barrier layers stacked alternately from bottom to top. The well layer is Al _x Ga _1-x N/Al _z In _y Ga _1-yz N/Al _x Ga _{1- x} N, where x=0.8, y=z=0.05. The barrier layer is AlN; the thickness of the _{AlzInyGa1 -yzN} layer in the well layer is 0.8nm, the total thickness of the two _{AlxGa1 -xN} layers _is 5nm, and the thickness of the barrier layer is 15nm.

Example 2

A DUV LED epitaxial wafer structure, including a substrate, on which, from bottom to top, a buffer layer composed of an AlN layer and an AlGaN/GaN superlattice, an n-AlGaN layer, a multi-quantum well light-emitting layer, and a p- AlGaN layer and p-GaN contact layer; the multi-quantum well light-emitting layer is composed of 10 pairs of well layers and barrier layers stacked alternately from bottom to top, and the well layer is Al _x Ga _1-x N/Al _z In _y Ga _1-yz N/Al _x Ga _1-x N, wherein x=0.6, y=z=0, and the barrier layer is AlN; the thickness of the Al _z In _y Ga _{1-y- z} N layer in the well layer is 1 nm, the total thickness of the two Al _x Ga _1-x N layers is 3 nm, and the thickness of the barrier layer is 10 nm.

Example 3

A DUV LED epitaxial wafer structure, including a substrate, on which there are AlN buffer layer, n-AlGaN layer, multi-quantum well light-emitting layer, p-AlGaN layer and p-GaN contact layer from bottom to top; The multi-quantum well light-emitting layer is composed of 20 pairs of well layers and barrier layers stacked alternately from bottom to top. The well layer is Al _x Ga _1-x N/Al _z In _y Ga _1-yz N/Al _x Ga _{1- x} N, where x=0.9, y=0, z=0.05, the barrier layer is AlN; the thickness of the Al _z In _y Ga _1-yz N layer in the well layer is 2nm, two layers of Al _x Ga _1-x N The total thickness of the layers is 2 nm, the thickness of the barrier layer is 5 nm.

Example 4

A DUV LED epitaxial wafer structure, including a substrate, on which there are AlN buffer layer, n-AlGaN layer, multi-quantum well light-emitting layer, p-AlGaN layer and p-GaN contact layer from bottom to top; The multi-quantum well light-emitting layer is composed of 20 pairs of well layers and barrier layers stacked alternately from bottom to top. The well layer is Al _x Ga _1-x N/Al _z In _y Ga _1-yz N/Al _x Ga _{1- x} N, where x=0.8, y=0.1, z=0, the barrier layer is AlN; the thickness of the Al _z In _y Ga _1-yz N layer in the well layer is 0.3nm, two layers of Al _x Ga _1-x The total thickness of the N layer is 4 nm, and the thickness of the barrier layer is 20 nm.

Claims (9)

1. A DUV LED epitaxial wafer structure, comprising a substrate, the upper surface of the substrate is successively a buffer layer, an n-AlGaN layer, a multi-quantum well light-emitting layer, a p-AlGaN layer and a p-GaN contact layer from bottom to top; It is characterized in that the multi-quantum well light-emitting layer is composed of several pairs of well layers and barrier layers alternately stacked from bottom to top, and the well layer is Al _x Ga _1-x N/Al _z In _y Ga _1-yz N /Al _x Ga _1-x N, where 0.6≦x≦0.9, the values of y and z should satisfy E _g (Al _z In _y Ga _1-yz N) < E _g (Al _x Ga _1-x N), The barrier layer is AlN _; the thickness of the _{AlzInyGa1 -yzN} layer in the well layer is 0.3-2nm, and the thickness of the well layer is smaller than that of the barrier layer. 2. A kind of DUV LED epitaxial wafer structure according to claim 1, is characterized in that, the total thickness of two layers of _{AlxGa1 -xN} layers in the well layer is 2～5nm, and the thickness of barrier layer is 5nm. ~20nm. 3. A DUV LED epitaxial wafer structure according to claim 1 or 2, wherein the buffer layer is an AlN buffer layer, or a buffer layer composed of an AlN layer and an AlGaN/GaN superlattice. 4. A DUV LED epitaxial wafer structure according to claim 1 or 2, characterized in that the number of periods of the well layer and the barrier layer in the multi-quantum well light-emitting layer is 1-20 pairs. 5 . A DUV LED epitaxial wafer structure according to claim 3 , wherein the number of periods of the well layer and the barrier layer in the multi-quantum well light-emitting layer is 1-20 pairs. 6. A kind of DUV LED epitaxial wafer structure according to claim 1 or 2, is characterized in that, the growth temperature of Al _x Ga _1-x N layer and Al _z In _y Ga _1- The growth temperature of _{the yz} N layer is the same. 7. A kind of DUV LED epitaxial wafer structure according to claim 3, is characterized in that, the growth temperature of Al _x Ga _1-x N layer and Al _z In _y Ga _1-yz N in the preparation process of multi-quantum well light-emitting layer The layers were grown at the same temperature. 8. A kind of DUV LED epitaxial wafer structure according to claim 4, is characterized in that, the growth temperature of Al _x Ga _1-x N layer and Al _z In _y Ga _1-yz N in the preparation process of multi-quantum well light-emitting layer The layers were grown at the same temperature. 9. A kind of DUV LED epitaxial wafer structure according to claim 5, is characterized in that, the growth temperature of Al _x Ga _1-x N layer and Al _z In _y Ga _1-yz N in the preparation process of multi-quantum well light-emitting layer The layers were grown at the same temperature.