PROPERTIES OF GRADED HAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.5GA1-XAS LAYERS GROWN BY MOLECULAR-BEAM EPITAXY

Modulation-doped In0.5Al0.5As/In0.5Ga0.5As heterostructures on composi tionally graded Inx0 less-than-or-equal-to x less-than-or-equal-to 0.5 Ga1-xAs buffer layers on (001) GaAs substrates were prepared by molec ular beam epitaxy. An investigation of samples is reported, which have different initial In compositions x0 = 0, 0.12, 0.18, 0.24, 0.5 in th e linearly graded buffer. The sample with x0 = 0.18 shows the highest electron mobility and the highest electron density, which are 9.3 x 10 (3) cm2 V-1 s-1 and 3 x 10(12) cm-2 at 300 K respectively, of the inve stigated samples. The smallest photoluminescence linewidth of 18 meV w as measured from both samples with x0 = 0.12 and 0.18. A small lattice tilt of 1.4 mrad between the relaxed In0.5Ga0.5As layer and substrate and a smooth surface was achieved for x0 = 0.18.