High room temperature hole mobility in Ge/sub 0.7/Si/sub 0.3//Ge/Ge/sub 0.7/Si/sub 0.3/ modulation doped heterostructures in the absence of parallel conduction

Abstract

Summary form only given. Recently, there has been a lot of interest in two dimensional hole gas systems in pure germanium channels, since Ge has the highest intrinsic bulk hole mobility of all the commonly used semiconductors, being comparable to the electron mobilities in bulk Si. Konig and Schaffler (IEEE Elec. Dev. Lett. vol. 14, p. 205, 1993) have reported a maximum extrinsic transconductance of 125 mS/mm (290 mS/mm) at 300 K (77 K) in these Ge channel FETs. However, the hole mobility achieved in these systems is limited by roughness scattering at the alloy-Ge interface at low temperatures and by parallel conduction at high temperatures. Engelhardt et al. (Solid State Electron. vol. 37, p. 949, 1994) have reported a maximum hole mobility of 1300 cm/sup 2//Vs at room temperature with channel density changing by about 50% from 4.2 K to 300 K, indicating the presence of parallel conduction. In order to measure the true hole mobility and identify the mobility limiting mechanism in the strained Ge channels, it is essential to overcome the contribution from the parallel channels due to the substrate and the doped supply layers. In this abstract, we report results on the mobility and carrier density of a two dimensional hole gas (2DHG) in strained Ge quantum wells with very low parallel conduction. We report a measured room temperature hole mobility in the Ge channel of 1700 cm/sup 2//Vs, which is the largest measured to date in these systems.