VARIATION OF BACKGROUND IMPURITIES IN ALXGA1-XAS (0.3 LESS-THAN-OR-EQUAL-TO X LESS-THAN-OR-EQUAL-TO 0.4) WITH GROWTH TEMPERATURE - IMPLICATIONS FOR DEVICE LEAKAGE CURRENT AND SURFACE HETEROINTERFACE ROUGHNESS

In a wide range of growth conditions, the residual impurity concentration is found to be higher in Al(x)Ga1-xAs (0.3 less-than-or-equal-to x less-than-or-equal-to 0.4) than in GaAs. Undoped AlGaAs is p-type for substrate growth temperature T(S) less-than-or-equal-to 680-degrees-C and n-type for T(S) approximately 700-degrees-C. In n-type Al0.33Ga0.67As, typical electron density and mobility were 5 x 10(14) cm-3 and 2340 cm2 V-1 s-1 at 300 K and 5 x 10(12) cm-3 and 8725 cm2 V-1 s-1 at 77 K, which we believe are the best values ever reported for this alloy. In p-type samples, hole density was less-than-or-equal-to 5 x 10(14) cm-3 at 300 K for T(S) = 580-degrees-C, and greater-than-or-equal-to 4 x 10(15) cm-3 for 600-degrees-C < T(S) less-than-or-equal-to 680-degrees-C. Photoluminescence (PL) intensity of near band to band emission at 1.5 K decreased with increasing T(S) from 580-degrees-C but increased dramatically with sharper peaks for T(S) > 680-degrees-C. Leakage current in 0.5-mu-m n+-GaAs/0.2-mu-m undoped-Al0.3Ga0.7As/n+-GaAs SIS heterostructure diodes increased with increasing T(S) of AlGaAs from 580-degrees-C to 620-degrees-C but decreased several orders of magnitude for T(S) = 700-degrees-C. Thus, Hall, PL and leakage current measurements suggest degradation of AlGaAs properties with increasing T(S) between 580 and 680-degrees-C but dramatic improvement for T(S) > 680-degrees-C. Misorienting the (100) GaAs substrates by 2-degrees-3-degrees towards <111>A also caused marked improvements in material quality in non-optimum growth conditions. For up to 5-mu-m thick AlGaAs, there is no "forbidden" range of growth temperature for misoriented substrates, but 10-mu-m thick layers were equally hazy on both type of substrates for 630 < T(S) < 680-degrees-C. For best performance, devices employing undoped AlGaAs should be grown at approximately 580-degrees-C or if structure permits at approximately 700-degrees-C.