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Structural,electrical and optical properties of in-situ phosphorous-doped Ge layers
Authors:JM Hartmann  JP Barnes  M Veillerot  JM Fédéli  Q Benoit A La Guillaume  V Calvo
Institution:1. CEA-LETI, Minatec Campus, 17, Rue des Martyrs 38054 Grenoble Cedex 9, France;2. CEA-INAC, 17, Rue des Martyrs 38054 Grenoble Cedex 9, France
Abstract:We have studied the impact of temperature and pressure on the structural and electronic properties of Ge:P layers grown with GeH4+PH3 on thick Ge buffers, themselves on Si(0 0 1). The maximum phosphorous atomic concentration P] exponentially decreased as the growth temperature increased, irrespective of pressure (20 Torr, 100 Torr or 250 Torr). The highest values were however achieved at 100 Torr (3.6×1020 cm?3 at 400 °C, 2.5×1019 cm?3 at 600 °C and 1019 cm?3 at 750 °C). P atomic depth profiles, “box-like” at 400 °C, became trapezoidal at 600 °C and 750 °C, most likely because of surface segregation. The increase at 100 Torr of P] with the PH3 mass-flow, almost linear at 400 °C, saturated quite rapidly at much lower values at 600 °C and 750 °C. Adding PH3 had however almost no impact on the Ge growth rate (be it at 400 °C or 750 °C). A growth temperature of 400 °C yielded Ge:P layers tensily-strained on the Ge buffers underneath, with a very high concentration of substitutional P atoms (5.4×1020 cm?3). Such layers were however rough and of rather low crystalline quality in X-ray Diffraction. Ge:P layers grown at 600 °C and 750 °C had the same lattice parameter and smooth surface morphology as the Ge:B buffers underneath, most likely because of lower P atomic concentrations (2.5×1019 cm?3 and 1019 cm?3, respectively). Four point probe measurements showed that almost all P atoms were electrically active at 600 °C and 750 °C (1/4th at 400 °C). Finally, room temperature photoluminescence measurements confirmed that high temperature Ge:P layers were of high optical quality, with a direct bandgap peak either slightly less intense (750 °C) or more intense (600 °C) than similar thickness intrinsic Ge layers. In contrast, highly phosphorous-doped Ge layers grown at 400 °C were of poor optical quality, in line with structural and electrical results.
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