Optical semiconductor device and manufacturing method therefor

Abstract

To provide an elemental technique for improving the emission intensity of deep ultraviolet light from a light emitting layer made of an AlGaInN-based material, in particular, an AlGaN-based material. First, an AlN layer is grown on a sapphire surface. The AlN layer is grown under a NH 3 -rich condition. The TMAl pulsed supply sequence includes growing an AlGaN layer for 10 seconds, interrupting the growth for 5 seconds to remove NH 3 , and then introducing TMAl at a flow rate of 1 sccm for 5 seconds. After that, the growth is interrupted again for 5 seconds. Defining this sequence as one growth cycle, five growth cycles are carried out. By such growth, an AlGaN layer having a polarity of richness in Al can be obtained. The above sequence is described only for illustrative purposes, and various variations are possible. In general, the Al polarity can be achieved by a process of repeating both growth interruption and supply of an Al source.

1 . A semiconductor structure, comprising:
 a polarity controlling layer, which is a first group III-V layer formed on a substrate under such a growth condition that the layer is formed to be rich in a group III element; and   a second group III-V layer formed on the polarity controlling layer.   
   
   
       2 . A semiconductor structure, comprising:
 a polarity controlling layer, which is a first group III nitride layer formed on a sapphire substrate under such a growth condition that the layer is formed to be rich in a group III element; and   a second group III nitride layer formed on the polarity controlling layer.   
   
   
       3 . The semiconductor structure according to  claim 2 , wherein said polarity controlling layer includes a group-III-rich layer formed by intermittently supplying a group III source in a state where a nitrogen source is not supplied, and a third group III nitride layer is formed between said substrate and said group-III-rich layer. 
   
   
       4 . The semiconductor structure according to  claim 3 , wherein said polarity controlling layer includes five or more group-III-rich layers. 
   
   
       5 . The semiconductor structure according to  claim 2 , wherein said group III source is TMAl. 
   
   
       6 . The semiconductor structure according to  claim 2 , wherein said polarity controlling layer has a structure in which a threading dislocation extending from the bottom turns around in the vicinity of the interface with said second group III-V layer. 
   
   
       7 . The semiconductor structure according to  claim 2 , further comprising:
 a high temperature grown AlN layer formed between said substrate and said first group III-V layer.   
   
   
       8 . The semiconductor structure according to  claim 2 , wherein said second group III-V layer is made of an InAlGaN-based semiconductor crystal. 
   
   
       9 . An optical semiconductor device having a semiconductor structure according to  claim 2 . 
   
   
       10 . The semiconductor device according to  claim 9 , wherein the semiconductor device is an optical semiconductor device that emits light at a wavelength ranging from 250 nm to 350 nm. 
   
   
       11 . A method of forming a semiconductor structure, comprising:
 a step of preparing a substrate; and   a step including a first period in which a group III source and a group V source are supplied to the substrate, a second period in which supply of the group III source and the group V source is stopped, a third period in which only the group III source is supplied and the group V source is not supplied, and a period in which said second and third periods are repeated to control the polarity of the surface to be a group III polarity.   
   
   
       12 . A method of forming a semiconductor structure, comprising:
 a step of preparing a substrate; and   a step including a first period in which a first Al source, a Ga source, and a N source are supplied to the substrate, a second period in which supply of all the sources is stopped, a third period in which only a second Al source is supplied, and a period in which said second and third periods are repeated to control the polarity of the surface to be an Al polarity.   
   
   
       13 . A method of forming a semiconductor structure, comprising:
 a step of preparing a sapphire substrate; and   a step including a first period in which a first Al source, a Ga source, and a N source are supplied to the sapphire substrate, a second period in which supply of all the sources is stopped, a third period in which only a second Al source is supplied, and a period in which said second and third periods are repeated to form a polarity controlling layer having a surface controlled to have an Al polarity.   
   
   
       14 . The method of forming a semiconductor structure according to  claim 13 , further comprising:
 a step of forming an AlN buffer layer between said sapphire substrate and said polarity controlling layer at high temperature.   
   
   
       15 . The method of forming a semiconductor structure according to  claim 13  or  14 , further comprising:
 a step of forming an optical semiconductor device made of InAlGaAs-based material on said polarity controlling layer.