Peak Hole Mobility Research Articles

High-mobility fully depleted thin-film SOS MOSFET's

Summary form only given. Transistor characteristics for improved, fully depleted thin-film (100-nm thick) silicon-on-sapphire (SOS) MOSFETs with 25-nm gate oxides were measured for various gate lengths from 15 to 300 K with measurements taken at 10 K intervals. Peak hole mobilities as high as 250 cm/sup 2//V-s at 300 K and 1700 cm/sup 2//V-s at 77 K were measured in p-channel MOSFETs. Measurements of corresponding n-channel devices of the same dimensions have revealed electron mobilities of 360 cm/sup 2//V-s at 300 K and 590 cm/sup 2//V-s at 77 K. The high hole mobility behavior unique to SOS may be attributed to stress in the thin silicon film due to the sapphire interface. >

Modulation doping in Ge(x)Si(1−x)/Si strained layer heterostructures: Effects of alloy layer thickness, doping setback, and cladding layer dopant concentration

Selectively doped GexSi1−x/Si strained layer heterostructures have been grown in a single quantum well configuration on 〈001〉-Si substrate using molecular beam epitaxy. The modulation doping effect has been observed in p-type structures only; although both n- and p-type double heterostructures were grown. We have investigated the effects of: (i) alloy layer thickness (well width), (ii) doping setback, and (iii) cladding layer dopant concentration, on the hole mobilities. At present, optimum structures show peak hole mobilities in excess of 3300 cm2V−1s−1 at 4.2 K, sheet charge densities of 3.0–14×1011 cm−2, and hole effective mass m*h =0.32±0.03 m0. It is found that the low temperature (T∼10 K) hole mobility, in structure having x=0.2 is relatively insensitive to alloy layer (well) thickness in the range 100 Å≲Lw≲Lc; where Lc is the critical thickness marking the transition from strained layer to relaxed, misfit accommodated, alloy growth. For Lw>Lc, misfit dislocation scattering dramatically decreases μh at T≲100 K; whereas for Lw≲100 Å the hole mobility is uniformly lowered over the entire range of measurement temperatures. Doping setback and cladding layer dopant concentration affect the mobility via changes in sheet charge density, in a manner consistent with theoretical expectations. The absence of the modulation doping effect in n-type heterostructure is taken as an indication that ΔEv≫ΔEc.

Modulation doping in GexSi1−x/Si strained layer heterostructures

We report the first observation of the modulation doping effect in Si/Ge0.2Si0.8 heterojunctions grown by molecular beam epitaxy. Peak hole mobilities of ∼3300 cm2 V−1 s−1 have been observed at 4.2 K. These values, although nonoptimum, are comparable to the best reported values for holes in Si/SiO2 inversion layers. Low temperature, angular dependent, Shubnikov–de Haas measurements have demonstrated the two-dimensional nature of the hole gas and yield a surface carrier density of 3.5×1011 cm−2. From the temperature dependence of the Shubnikov–de Haas amplitudes a hole effective mass of 0.30±0.02mo has been derived. Identical measurements on n-type heterojunctions having the same Ge content (x=0.2) have failed to show a sustained enhancement of mobility at low temperatures, indicating that ΔEv≫ΔEc.