COMPOSITION DEPENDENT TRANSPORT-PROPERTIES OF STRAIN RELAXED INXGA1-XAS(X-LESS-THAN-OR-EQUAL-TO-0.45) EPILAYERS

The concentration and mobility of the two-dimensional electron gas present at the interface between strain-relaxed, lattice matched, InyAl1-yAs/InxGa1-xAs(x < 0.45), modulation doped heterojunctions grown by means of compositionally step-graded buffer layers on GaAs substrates, were measured at room temperature and at 77 K. The composition dependence of the electron density is attributed to the dependence of the band-gap energy of InxGa1-xAs and that of InyAl1-yAs on x, with a conduction band offset, DELTA-E(c) approximately 0.67-DELTA-E(g). The room temperature electron mobility increases from 9 x 10(3) cm2/V s for x = 0.07 to 1.05 x 10(4) cm2/V s for x = 0.45. Such strain-relaxed heterostructures have higher electron mobilities than similar pseudomorphic structures with the same sheet electron concentration.