Method for growing an epitaxial layer of CdTe on an epitaxial layer of HgCdTe grown on a CdTe substrate

A liquid-phase-epitaxial method for growing a CdTe epitaxial layer on a HgCdTe epitaxial layer that has been grown on a CdTe substrate that has been mechanically and chemically polished, said method comprising:

• (i) preparing a CdTe substrate with a predetermined oriented surface selected from the surfaces of (100), (110), (111)Cd, and (111)Te by lapping said substrate with a 3200 mesh abrasive, chemically polishing with a Br.sub.2 :HBr.sub.2 solution of about 2% bromine by volume, cleaning in deionized water, trichloroethylene, acetone, and methanol in an ultrasonic cleaner, and finally by etching with a solution of about 5% by volume bromine in methanol to remove the polishing damage;
• (ii) reacting in accordance with a first predetermined temperature profile an appropriate amount of high purity (99.9999%) Hg, Cd, and Te in a first melt composition, said first melt composition being CdTe:Hg:Te in ratio 0.004:0.251:0.745 which is contained in a first high pressure liquid-epitaxial-growth system apparatus comprising an inner quartz reaction tube and an outer quartz tube mounted in a vertical furnace that is controlled to within .+-.0.05.degree. C., said outer quartz tube mounted between two stainless steel flanges to keep high argon gas pressure and to control the high mercury vapor pressure over said first melt composition containing said CdTe, Hg, and Te, said reacting in accordance with said first predetermined temperature profile including a heat-up time period of about 40 minutes from ambient temperature to a temperature of about 700.degree. C. which is the reacting temperature of said first predetermined temperature profile that is maintained for a time period of about one hour;
• (iii) reducing said reacting temperature of said first melt composition to about 550.degree. C. which is the melt back temperature of said first predetermined temperature profile;
• (iv) inserting said prepared CdTe substrate that is retained on a quartz sample holder into said first melt composition to allow said prepared CdTe substrate to melt back for about 15 seconds to eliminate a Hg vapor diffusion layer obtained during said heat-up time period and then reducing said temperature to the liquid-epitaxial-growth temperature which initially starts the growth time at a temperature within about 15.degree. C. of the saturated or unsaturated temperature of said first melt composition, and said growth time taking place over a period of up to about 30 minutes;
• (v) growing an epitaxial layer on said selected oriented surface of said substrate at a rate of about 1 micrometer per .degree.C. as the growth temperature drops at a rate of from about 0.2 to about 1.degree. C. per minute, said epitaxial layer being a layer of Hg.sub.1-x Cd.sub.x Te on said selected oriented surface of said substrate of a predetermined thickness, with x being a value from about 0.17 to about 1.0 so that some mercury is always present in Hg.sub.1-x Cd.sub.x Te layer, during said liquid-epitaxial-growth temperature period of said first predetermined temperature profile;
• (vi) removing said inserted CdTe substrate retained on said quartz sample holder from said first melt composition and reducing the temperature at the completion of said liquid-epitaxial-growth temperature period to ambient temperature during a cool down period of said first predetermined temperature profile of from about 2 to about 3 hours;
• (vii) positioning said substrate with said grown epitaxial layer of said Hg.sub.1-x Cd.sub.x Te in a second high pressure liquid-epitaxial-growth system apparatus which is loaded with a predetermined amount of a high purity (99.9999%) materials of Sn, Hg, and CdTe in a ratio of Sn:Hg:CdTe which equals 36:5:0.15, said materials forming a growth solution when molten for the growth of an epitaxial layer of CdTe on said epitaxial layer of said Hg.sub.1-x Cd.sub.x Te;
• (viii) reacting in accordance with a second predetermined temperature profile said materials of Sn:Hg:CdTe to form a second melt composition which is contained in a said second high pressure liquid-epitaxial-growth system apparatus of a like set-up defined for said first high pressure liquid-epitaxial-growth system apparatus, said reacting in accordance with said second predetermined temperature profile including a heat-up time period of about 40 minutes from ambient temperature to a temperature of about 700.degree. C. which is the reacting temperature of said second predetermined temperature profile that is maintained for a time period of about one hour;
• (ix) reducing said reacting temperature of said second melt composition from about 700.degree. C. to about 525.degree. C. which is the starting temperature for CdTe epitaxial layer growth;
• (x) inserting said substrate with said grown epitaxial layer of said Hg.sub.1-x Cd.sub.x Te into said second melt composition and supercooling said second melt composition at a rate from about 1.degree. C. to about 5.degree. C. per minute which is necessary to avoid melting said epitaxial layer of said Hg.sub.1-x Cd.sub.x Te during the epitaxial growing of a CdTe layer on said Hg.sub.1-x Cd.sub.x Te;
• (xi) growing an epitaxial layer of CdTe on said Hg.sub.1-x Cd.sub.x Te layer as the growth temperature drops during said supercooling at said rate from about 1.degree. C. to about 5.degree. C. per minute to complete a supercooling temperature range greater than 15.degree. C. and an epitaxial layer of CdTe of a few micrometers thickness;
• and
• (xii) removing said inserted substrate with said grown epitaxial layers of Hg.sub.1-x Cd.sub.x Te and CdTe thereon from said second melt composition and reducing the temperature at the completion of said liquid-epitaxial-growth temperature period to ambient temperature during a cool down period of said predetermined temperature profile of from about 2 to about 3 hours.