Semiconductor crystal substrate, infrared detector, method for producing semiconductor crystal substrate, and method for producing infrared detector
A semiconductor crystal substrate includes a crystal substrate that is formed of a material including one of GaSb and InAs, a first buffer layer that is formed on the crystal substrate and formed of a material including GaSb, and a second buffer layer that is formed on the first buffer layer and formed of a material including GaSb. The first buffer layer has a p-type conductivity, and the second buffer layer has an n-type conductivity.
1. A method of producing a semiconductor crystal substrate, the method comprising:
forming a first buffer layer on a crystal layer by molecular beam epitaxy with a material including GaSb, the crystal layer being formed of a material including one of GaSb and InAs, a composition ratio of Ga in the first buffer layer being greater than a composition ratio of Sb in the first buffer layer, and the first buffer layer having a p-type conductivity; and
forming a second buffer layer on the first buffer layer by molecular beam epitaxy with a material including GaSb, a composition ratio of Sb in the second buffer layer being greater than a composition ratio of Ga in the second buffer layer, and the second buffer layer having an n-type conductivity, wherein
the first buffer layer is formed at a substrate temperature greater than or equal to 470° C. and less than or equal to 550° C.; and
the second buffer layer is formed at a substrate temperature greater than or equal to 420° C. and less than or equal to 460° C.
2. The method as claimed in claim 1 , wherein the first buffer layer is formed at a substrate temperature greater than or equal to 500° C. and less than or equal to 550° C.
3. The method as claimed in claim 1 , wherein the molecular beam epitaxy is solid source molecular beam epitaxy.
4. The method as claimed in claim 1 , wherein
the first buffer layer is formed of the material including GaSb and one or both of In and As; and
the second buffer layer is formed of the material including GaSb and one or both of In and As.
5. A method of producing an infrared detector, the method comprising:
forming a first contact layer having the n-type or p-type conductivity on the second buffer layer of the semiconductor crystal substrate produced by the method of claim 1 ;
forming an infrared absorption layer having a superlattice structure on the first contact layer; and
forming a second contact layer having the other of the n-type or the p-type conductivity on the infrared absorption layer.
6. The method as claimed in claim 5 , wherein
the first contact layer is p-type, and the first contact layer is formed of a material including GaSb;
the infrared absorption layer having the superlattice structure is formed by alternately stacking a GaSb layer and an InAs layer; and
the second contact layer is n-type, and the second contact layer is formed of a material including InAs.