CRITICAL LAYER THICKNESS IN ALGAASSB GASB HETEROSTRUCTURES DETERMINEDBY X-RAY-DIFFRACTION/

The critical thickness of strained AlxGa1-xAsySb1-y layers (0.35 less- than-or-equal-to x less-than-or-equal-to 0.58) grown by liquid phase e pitaxy (LPE) on GaSb (001) oriented substrates was determined by X-ray double-crystal diffractometry on (115) reflection planes. This method allows one to determine the relative lattice-mismatch perpendicular t o the growth direction (DELTAa/a)perpendicular-to and in the junction plane (DELTAa/a)parallel-to. The state of the epitaxial layer (straine d or relaxed) was deduced for mismatches (DELTAa/a)0 = (a(AlGaAsSb) - a(GaSb))/a(GaSb) varying from - 1 X 10(-3) to 4 x 10(-3). The evaluate d critical thickness of layers under tension was: h(c) (mum) almost-eq ual-to 0.4 x 10(-3)/(DELTAa/a)0 much lower than that of layers under c ompression: h(c) (mum) almost-equal-to 2.2 x 10(-3)/(DELTAa/a)0.