US 2015/0028286 A1Published application

Method for growing germanium/silicon-germanium superlattice

AssigneeBAE Systems Information and Electronic Systems Integration Inc.

InventorsVu Anh Vu, Sandra L. Hyland, Robert L. Kamocsai, Daniel J. O'Donnell, Andrew T. Pomerene

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Abstract

A bulk manufacturing method for growing silicon-germanium stained-layer superlattice (SLS) using an ultra-high vacuum-chemical vapor deposition (UHV-CVD) system and a detector using it is disclosed. The growth method overcomes the stress caused by silicon and germanium lattice mismatch, and leads to uniform, defect-free layer-by-layer growth. Flushing hydrogen between the layer growths creates abrupt junctions between superlattice structure (SLS) layers. Steps include flowing a mixture of phosphine and germane gases over a germanium seed layer. This in-situ doped germanium growth step produces an n-doped germanium layer. Some of the phosphorus diffuses into the underlying germanium and reduces the stress in the underlying germanium that is initially created by the lattice mismatch between germanium and silicon. Phosphine can be replaced by diborane if a p-doped layer is desired. The reduction of stress results in a smooth bulk germanium growth.

Claims20

Dependent claims

A method of growing a germanium/silicon-germanium superlattice structure (SLS) comprising the steps of:

(a) preconditioning a silicon substrate with hydrogen gas with a pressure at most equal to approximately 3E−4 mBar;
(b) reducing temperature and pressure;
(c) providing germane gas with a pressure at most equal to approximately 5E−4 mBar flowing over said silicon substrate to form a germanium seed layer;
(d) heating in approximately a vacuum;
(e) flowing gasses with a pressure at most equal to approximately 5E−4 mBar over said germanium seed layer to form a doped germanium layer;
(f) flowing germane gas with a pressure at most equal to approximately 5E−4 mBar over said germanium layer forming a first buffer;
(g) flowing at least germane gas over said first buffer with a pressure at most equal to approximately 5E−4 mBar, forming a layer of single-crystal comprising at least germanium;
(h) flushing with hydrogen or allowing to remain idle;
(i) flowing at least one gas over said single-crystal comprising at least germanium layer with a pressure at most approximately 5E−4 mBar, forming a subsequent layer of single-crystal comprising at least germanium;
(j) flushing with hydrogen or allowing to remain idle;
(k) repeating said steps (g) through (j) multiple times, forming SLS layers, wherein silicon content of alternate layers varies;
(1) flowing germane gas with a pressure at most equal to approximately 5E−4 mBar over a germanium layer forming a second buffer;
and
(m) flowing gasses with a pressure at most equal to approximately 5E−4 mBar over said second buffer to form a doped layer.

11 more elements

A method of growing a germanium/silicon-germanium superlattice structure (SLS) comprising:

(a) preconditioning a silicon substrate with hydrogen gas at approximately 750° C. for 60 minutes with a pressure approximately equal to 3E−4 mBar;
(b) reducing temperature to 350° C. at the rate of 2° C./min while maintaining vacuum as in (a);
(c) flowing germane gas with a pressure equal to approximately 5E−4 mBar over said silicon substrate for approximately 120 minutes to form a germanium seed layer;
(d) heating said germanium seed layer at approximately 2° C./min to approximately 600° C. while maintaining vacuum as in (c);
(e) flowing phosphine and germane gasses at a ratio of approximately 1:3 respectively with a pressure approximately equal to 5E−4 mBar over said germanium seed layer for approximately 10 minutes to form an n-doped germanium layer;
(f) flowing germane gas with a pressure approximately equal to 5E−4 mBar over said n-doped layer for approximately 20 minutes to grow a first buffer layer of germanium;
(g) flowing at least germane gas with a pressure approximately equal to 5E−4 mBar for approximately 1 minute to form a layer of single-crystal comprising at least germanium;
(h) flushing with hydrogen or allowing to sit idle under vacuum for approximately 2 minutes so that an abrupt junction will form when silicon-germanium is later grown on the existing germanium;
(i) flowing a 4:1 mixture of silane and germane gases with a pressure of approximately 5E−4 mBar for approximately 90 seconds to grow a layer of silicon-germanium on said layer of single-crystal comprising at least germanium;
(j) flushing with hydrogen or allowing to sit idle under vacuum for approximately 2 minutes so that an abrupt junction will form when germanium is later grown on the existing silicon-germanium;
(k) repeating said steps (g) through (j) multiple times, forming SLS layers;
(l) flowing germane gas with a pressure approximately equal to 5E−4 mBar for approximately 20 minutes to grow a second buffer layer of single-crystal germanium on said layer of silicon-germanium;
and
(m) flowing diborane and germane gasses in a ratio of approximately 1:50 respectively with a pressure approximately equal to 5E−4 mBar for approximately 30 minutes over said second buffer to form a p-doped layer.

11 more elements

Dependencies are inferred from the claim text.