INFLUENCE OF SUBSTRATE-TEMPERATURE ON ELECTRON-MOBILITY IN NORMAL AND INVERTED SINGLE PERIOD MODULATION DOPED ALXGA1-XAS/GAAS HETEROJUNCTIONS

SINGLE PERIOD MODULATION DOPED AL//XGA//1// - //XAS/GAAS HETEROSTRUCTURES WERE GROWN BY MOLECULAR BEAM EPITAXY USING A SUBSTRATE TEMPERATURE RANGE OF 580-750 D. C. EXCELLENT SURFACE MORPHOLOGIES WERE ROUTINELY OBTAINED THROUGHOUT THE ENTIRE RANGE OF SURFACE TEMPERATURES. THE HIGHEST MOBILITIES OBTAINED FOR STRUCTURES WITH THE AL//XGA//1// - //XAS/GAAS ON TOP OF THE GAAS WERE 9000, 133000, AND 282000 CM**2/V S AT 300, 78, AND 10 K, RESPECTIVELY. THE SHEET CARRIER CONCENTRATION YIELDING THE BEST ELECTRON MOBILITY WAS ABOUT 8 * 10**1**1CM** - **2. WHILE THE MOBILITIES WERE INDEPENDENT OF SUBSTRATE GROWTH TEMPERATURE BETWEEN 600 AND 675 D. C, SOME DEGRADATION WAS OBSERVED OUTSIDE THIS RANGE. STRUCTURES WITH THE GAAS ON TOP OF THE AL//XGA//1// - //XAS EXHIBITED MOBILITIES AS HIGH AS 35 400 CM**2/V S AT 10 K WHEN GROWN NEAR A SUBSTRATE TEMPERATURE OF 720 D. C. MOBILITY ENHANCEMENT WAS NOT OBSERVED IN SAMPLES GROWN AT TEMPERATURES WELL BELOW 700 D. C.