Maximum-entropy mobility spectrum of two-dimensional hole gas in strained-Si_1_-_xGe_x/Si heterostructures

Magnetotransport properties of modulation-doped p-type Si_1_-_xGe_x/Si and Si_1_-_xGe_x/Si_1_-_yGe_y heterostructures were studied, in the magnetic field range 0-12 T, and in the temperature range 0.35-300 K. The experimental data within the classical regime have been analysed by mobility spectrum analysis, in order to separate the influences of different parallel conduction paths. A new method of mobility spectrum analysis has been developed by the author, based on the concept of maximum-entropy, and this computation has been shown to overcome several drawbacks or limitations of previous mobility spectrum methods of calculation. The data have also been analysed by Beck and Anderson's analysis and the multicarrier fitting method for comparison. Analysis of the magnetic-field-dependent resistivity tensors reveals a two-dimensional hole gas (2DHG) in the Si/SiGe/Si quantum well, carriers in the boron-doped cap layer, and an unknown electron-like carrier. The carrier density of the 2DHG can either remain constant (x = 0.1), increase (x = 0.13), or decrease (x #>=# 0.2), with increasing temperatures. Differences in the temperature dependences are partly attributed to different growth conditions. A decreasing carrier density with increase in temperatures may indicate the presence of acceptor-like defect states near the valence band edge of the SiGe channel. The mobility of the 2DHG between 100-300 K has the form AT"-"#gamma# and #gamma# has the bowl shape with the minimum at x #approx# 0.25-0.3. These characteristics suggest a possible influence of alloy disorder scattering. The mobilities and activation energies of the carriers in the boron-doped cap vary between samples and this is believed to be due to boron-spike near the Si/Si-substrate interface, in some samples. The source of electron-like carrier is presently unknown. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN044187 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Ultra high hole mobilities in a pure strained Ge quantum well

Hole mobilities at low and room temperature (RT) have been studied for a strained sGe/SiGe heterostructure using standard Van der Pauw resistivity and Hall effect measurements. The range of magnetic field and temperatures used were − 14 T 3 cm2/V s was determined for a sheet density (ps) 9.8 × 1010 cm-2 (by ME-MSA) and (3.9 ± 0.2) × 103 cm2/V s for a sheet density (ps) 5.9 × 1010 cm-2 (by BAMS)

New RP-CVD grown ultra-high performance selectively B-doped pure-Ge 20 nm QWs on (100)Si as basis material for post-Si CMOS technology

Magnetotransport studies at low and room temperature are presented for two-dimensional hole gases (2DHG) formed in fully strained germanium (sGe) quantum wells (QW). Two designs of modulation doped heterostructure grown by reduced pressure chemical vapour deposition (RP-CVD) were used and included a normal structure (doping above the Ge channel and inverted structure (doping beneath the Ge channel). The mobility (μH) for the normal structure was measured to be 1.34×106 cm2/Vs with a sheet density (ps) of 2.9×1011cm-2at 1.5 K, and μH= 3970 cm2/Vs and ps ∼1×1011cm-2 for room temperature, determined from simulation using the Maximum Entropy-Mobility Spectrum Analysis (ME-MSA) method. For the inverted structure a μH of 4.96×105 cm2/Vs and ps of 5.25×1011cm-2was measured at 90 mK. From the temperature dependent amplitude of Shubnikov de Haas oscillations, the normal structure was found to have a very low effective mass (m*) value of 0.063 m0 and a ratio of transport to quantum lifetime (α) of ∼78. This extremely high α is indicative of the carrier transport being dominated by small angle scattering from remote impurities i.e. a sample having an extremely low background impurity level and very smooth hetero-interfaces. The inverted structure had an m*of 0.069 m0 and α ∼29, which also indicates exceedingly high quality material