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We have observed Shubnikov-de Haas oscillations in the longitudinal magnetoresistance of SnTe, a cubically symmetric, extrinsic ptype semiconductor. 1 " 5 The measurements were made in steady magnetic fields up to 155 kG. Oscillations were detected between 40 and 155 kG, and were seen in samples with carrier concentrations 6 /) between 5xl0 19 and 5xl0 20 cm" 3 . It is very unusual to have observed the Shubnikov-de Haas effect over such a wide range of carrier concentrations. Moreover, the upper limit is some 25 times larger than the highest concentration at which such oscillations have been detected previously in an extrinsic material. 7 It was possible to observe the oscillations at such large carrier concentrations because of the high magnetic field intensities available, and because of the extraordinarily weak "ionized impurity" scattering 8 in SnTe.The results presented here already suggest (1) the orientation of the Fermi surfaces, (2) the presence of a second, lower-lying valence band, and (3) an explanation for several puzzling electrical and elastic measurements obtained earlier. 2 ' 6 ' 9For our as-pulled single crystals, />«5xl0 20 cm"" 3 . We obtained lower p values by diffusion techniques to be described elsewhere. The crystallographic orientations studied included [001], [114], [112], [111], and [110] directions. Measurements were made at 4.2 and 1.4°K. The high, steady magnetic fields were produced in a li-inch inner diameter modified Bitter-type solenoid. 10

The conversion of semi-insulating GaAs to p type as a result of heat treatment in H2 was studied by photoluminescence (PL), secondary-ion mass spectrometry (SIMS), and transport measurements. The SIMS measurements resulted in the direct chemical identification of Mn near the heated surface. The correlation of the SIMS profiles with the results of PL and transport measurements indicated that Mn acceptors are responsible for the type conversion, and that substantial concentrations of Mn(?1017/cm3) are found in thin (1–3 μm) layers near the surface. The results of studies of samples heated under several different conditions showed that the Mn layers were not introduced by contamination from external sources during heat treatment, but were probably due to the presence of a bulk Mn concentration (<3×1015/cm3): during heat treatment the Mn diffuses to the surface, probably assisted by the in diffusion of Ga vacancies, as suggested by Zucca. Photoluminescence profiling measurements and the correlation between the SIMS and PL results indicate that the 1.41-eV PL band that is associated with the type-converted surface is due to recombination at a Mn acceptor on a Ga site, and not at a next-nearest-neighbor arsenic vacancy-amphoteric acceptor complex.

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