M. D. Moldavskaya

Shallow acceptors in Ge/GeSi multi-quantum well heterostructures

Abstract The experimental spectra of residual shallow acceptors in strained quantum well Ge/GeSi heterostructures are interpreted on the basis of a new theoretical approach taking into account both confinement and strain effects. It is shown that the main lines in the spectra of undoped samples with narrow quantum wells result from the photoexcitation of the on-edge acceptors that have binding energy two times less than on-center acceptors.

Far-Infrared Spectroscopy of Shallow Acceptors in Strained Ge/GeSi Quantum Well Heterostructures

Far-infrared photoconductivity spectra of strained multi-quantum well Ge/Ge1—xSix (≈ 0.1) heterostructures resulting from the excitation of shallow acceptors were investigated. The spectra are shown to be shifted to the long-wavelength end of the far-infrared range if compared with acceptors in bulk p-Ge due to the splitting of light and heavy holes subbands in Ge layers owing to the “built-in” deformation and size quantization. The shallow acceptor spectra in bulk germanium under uniaxial tension, that is “equivalent” to the deformation of Ge layers in the heterostructures, were calculated by the variational technique; the results were used for the interpretation of the experimental data. Ge/GeSi heterostructures are shown to be a sensitive photoelectric detector for the long wavelength end of FIR range.

Cyclotron Resonance in Ge Layers of Ge1-xSix–Ge Strained Heterostructures

Cyclotron resonance of photoexcited carriers in Ge/Ge1-x Six multilayer strained undoped heterostructures (HSs) was investigated for the first time. Cyclotron resonance line of positive charge carriers with the effective mass m c≈0.07m0 corresponding to that of holes in the upper subband in the strained quantum wells in Ge layers was observed in the absorption and mm-photoconductivity spectra. The persistent photoconductivity is shown to arise after interband illumination owing to the free holes remaining in the sample.

Shallow acceptors in strained multiquantum-well Ge/Ge1−xSix heterostructures

Far infrared photoconductivity spectra due to excitation of shallow acceptors in strained multiquantum well Ge/Ge1−xSix (x≈0.1) heterostuctures are investigated. It is shown that these spectra are shifted toward longer wavelengths in the far infrared region compared with those of bulk p-Ge, owing to “built-in” strain and size quantization, which lead to splitting of the light-and heavy-hole subbands in the Ge layers. Shallow acceptor spectra are calculated variationally for bulk germanium under uniaxial tension, which is “equivalent” to the strained Ge layers in the heterostructures. Although this method is only appropriate for wide quantum wells (dGe≈800 Å), the calculations are shown to qualitatively account for photoconductivity spectra obtained from narrower wells (dGe≈200 Å) as well.

Hot Hole Effects in Strained Mqw Heterostructures Ge/Ge1−xSix

The paper deals with the first investigations of the 2D hot hole effects in multilayer heterostructures Ge/Ge1−xSix aimed at the realization of dynamical heating and intraband population inversion of carriers in strong electric fields. Ge/Ge1−xSix heterostructures (x ≈ 0.1, dGE ≈ 200 A) were grown on Ge(lll) substrates by CVD technique. In these heterostructures the quantum wells in the valence band are realized in thin germanium layers which are uniformly compressed in the plane of the structure because of the mismatch of lattice periods of Ge and GeSi. The deformation may be represented as a result of hydrostatic compression and equivalent uniaxial tension of Ge layers; the latter is responsible for the valence band splitting. Earlier we have observed in undoped heterostructures the CR line of photoexcited 2D holes (m c ≈ 0.07m 0) in 2-mm wavelength range at liquid helium temperature1. The halfwidth of CR line corresponds to the high value of the hole mobility μ ≈ 105 cm2/V·s thus testifying the quality of the heterostructures.

Hot Hole Effects in Strained Multi-Quantum-Well Heterostructures Ge/GeSi

Last years strained heterostructures on base Ge and Si are of considerable interest due to wide range of properties which can be changed through band-structure engineering. We deal with heterostructures Ge/Ge1-xSix (x ≈ 0.1, dGe ≤ 200A) which were grown on moderately doped Ge (111) substrates by CVD techique. In these heterostructures quantum wells in the valence band are realized in germanium layers while the energy structure of conductance band is not quite clear yet. Theoretical calculations of the energy spectra give the negligible value of the conductance band offset (it seems to be the reason of the absence of the electron effects in the our experiments) while in the valence band the depth of the quantum well is about 100 meV. Ge layers are uniformly compressed in the plane of the structure because of the mismatch of lattice periods of Ge and Ge/Ge1-xSix This deformation may be represented as a result of hydrostatic compression and equivalent uniaxial tension PeqUiv of Ge layers; the latter is responsible for the valence band splitting. Earlier we have observed the cyclotron resonance (CR) absorption line of high mobility light 2D holes in split valence band in Ge layers [1] and revealed the electric field effects on the hole systems [2]. In this paper we report the further investigation of hot hole CR, that give mush information about the heating and energy spectrum of 2D holes . Also hot hole far infrared emission from selectively doped heterostructures was observed. The results of this experiment are shortly discussed.

Hot Hole p-Ge Lasers and Masers for Spectroscopy of MultiQuantum-Well Heterostructures Ge/Ge1-xSix

Hot hole p-Ge masers and lasers operating in millimiter and far IR ranges (up to 100 μm) belong to a new group of tunable semiconductor generators discovered in the early ’80s(1). They are proposed to be used in solid state spectroscopy since their discovery. These generators may be preferable to other sources of the same frequency since it is possible to set the sourcer of radiation near by the sample and provide ultralow background radiation conditions in low temperature experiments.The performance of the tunable spectrometer with hote hole p-Ge emitter is demostrated by its application to studies of cyclotron resonance in strained multi-quantum-well (MQW) heterostructures (HS) Ge/Ge0.87Si0 13 and investigations of shallow impurities in these heterostructures.