Very high hole mobilities in modulation-doped Ge quantum wells grown by low-energy plasma enhanced chemical vapor deposition

Abstract

We report on the fabrication of modulation-doped compressively strained Ge quantum wells by low-energy plasma enhanced chemical vapor deposition. A virtual substrate consisting of a thick linearly graded SiGe buffer layer and a cap layer of constant composition is first grown at a high rate (>5 nm/s). The active layer stack, grown at a reduced rate, contains strain compensating cladding layers with modulation doping above the channel. Mobilities of up to 3000 cm2/V s and 87 000 cm2/V s have been achieved at room temperature and liquid He temperature, respectively.

Acoustoelectric effects in very high-mobility p-SiGe/Ge/SiGe heterostructure at low temperatures in high magnetic fields

“…3 The buffer, graded at a rate of about 10%/µm to a final Ge content of 70%, and the 4 µm thick constant composition layer were grown at a high rate of 5-10 nm/s while gradually lowering the substrate temperature T s from 720 o C to 450 o C. The active layer structure, consisting of a pure 20 nm thick Ge layer sandwiched between cladding layers with a Ge content of about 60% and a Si cap, was grown at a low rate of about 0.3 nm/s at T s = 450 o C. Modulation doping was achieved by introducing dilute diborane pulses into the cladding layer grown above the channel after an undoped spacer layer of about 30 nm.…”

“…Here we studied the p-SiGe/Ge/SiGe sample (K6016) the conductivity of which was investigated earlier by direct current 3 and SAW. 1 The layer structure of the sample is illustrated in Fig.…”

Application of Bryan’s algorithm to the mobility spectrum analysis of semiconductor devices

“…In this manner, structures can be designed in which charge carriers are confined in a quantum well physically remote from the dopant atoms they originate from; ionized impurity atoms can strongly limit the mobility of charge carriers so this method of modulation doping can lead to greatly enhanced transport properties. [2,3,4] However, the physics of magnetotransport in such heterostructures is considerably more complicated if there are two or more distinct carrier gases present in the material (for example, the intended carrier gas in the quantum well plus the doped region) or the carrier gases feature a spread of mobilities due to energy-dependent scattering mechanisms or multiple subband occupancy. This leads to resistivities and Hall coefficients which are dependent on the applied magnetic field, and to extract the properties of such systems the simple single-carrier model is * Electronic address: daniel@chrastina.net; Current address: INFM and L-NESS Dipartimento di Fisica, Politecnico di Milano, Polo Regionale di Como, Via Anzani 52, I-22100 Como, Italy † Current address: Department of Physics, University of Cincinnati, OH 45221-0011 not sufficient.…”

“…To this end, various mobility spectrum techniques have been employed. [3,4,5,6] In a seminal paper, based on the work of McClure, [7] Beck and Anderson [8] showed that the conductivity tensor depends on a generalized conductivity function, s(µ), via the integral transforms,…”

High mobility holes in a strained Ge quantum well grown on a thin and relaxed Si0.4Ge0.6/LT-Si0.4Ge0.6/Si(001) virtual substrate

“…Indeed, very high 2DHG mobilities in the range 2400-3100 cm 2 V −1 s −1 with carrier densities of 5 -41ϫ 10 11 cm −2 have become routinely achievable in 7.5-25 nm thick Ge QWs. [1][2][3] Until now, very high mobility holes were only obtained in strained Ge QWs grown on relatively thick ͑1-8 m͒, high Ge content, Si 1−x Ge x buffers. 2,3 However, the low thermal conductivity of undoped SiGe is a drawback for nanoscale metal oxide semiconductor field effect transistor ͑MOSFET͒ and modulation doped semiconductor field effect transistor ͑MODFET͒ device applications.…”