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当用烷氧基硅酸盐和磷酸盐在本征 GaAs 的表面上生长一层 SiO_2或磷硅玻璃(PSG)时,掺 Cr 的本征 GaAs 表面附近形成一薄的导电层。导电层的厚度随热处理的时间和温度的增加而增厚,此导电层为 n 型,其电子浓度和迁移率分别为1～2×10~(17)厘米~(-3)和2500厘米~2/伏·秒。归纳起来,导电层形成的原因是本征 GaAs 中补偿不希望的施主的 Cr 浓度,因它向氧化膜中扩散而浓度减小。用从石英溅射生成的SiO_2或 Si_3N_4复盖本征 GaAs 就可以避免形成这样的导电层,Cr 在本征 GaAs 中扩散系数的激活能为3.6电子伏。
When a layer of SiO 2 or phosphosilicate glass (PSG) is grown on the surface of intrinsic GaAs with alkoxysilicates and phosphates, a thin conductive layer is formed near the Cr-doped intrinsic GaAs surface. The thickness of the conductive layer is increased with the increase of the time and temperature of the heat treatment. The conductive layer is n-type. The electron concentration and the mobility of the conductive layer are respectively 1~2 × 10 ~ (17) cm ~ (-3) and 2500 cm ~ 2 / V · second. To sum up, the reason for the formation of the conductive layer is that the concentration of Cr in the intrinsic GaAs to compensate for the undesired donor is decreased due to its diffusion into the oxide film. The formation of such a conductive layer can be avoided by coating intrinsic GaAs with Si02 or Si3N4 formed by sputtering of quartz, and the activation energy of diffusion coefficient of Cr in intrinsic GaAs is 3.6 electron volts.