Search

Photoconductivity spectra in a HgTe/CdHgTe double quantum well with a normal band structure have been studied. Photosensitivity bands associated with the ionization of a mercury vacancy, which is a doubly charged acceptor, have been detected in photoconductivity spectra. The transformation of photoconductivity spectra when the Fermi level moves from the edge of the valence band through the band gap to the conduction band has been revealed using the residual photoconductivity effect. It has been shown that the observed absorption bands are due to the ionization of doubly charged acceptors rather than individual different singly charged states. [ABSTRACT FROM AUTHOR]

A long-wavelength band caused by transitions between states related to the valence band is detected in the photoconductivity spectra of HgTe/CdHgTe (CMT) structures with quantum wells. The energy states of mercury vacancies in quantum wells of CMT structures is calculated taking into account a chemical shift. It is shown that the long-wavelength band observed in the photoconductivity spectra of these structures is associated with the ionization of divalent acceptor centers which are such vacancies. [ABSTRACT FROM AUTHOR]

The photoconductivity (PC) spectra of CdHgTe (MCT) solid solutions with a Cd fraction of 17 and 19% are measured. A simple model for calculating the states of doubly charged acceptors in MCT solid solutions, which makes it possible to describe satisfactorily the observed photoconductivity spectra, is proposed. The found lines in the photoconductivity spectra of narrow-gap MCT structures are associated with transitions between the states of both charged and neutral acceptor centers. [ABSTRACT FROM AUTHOR]

A theoretical model developed for interpretation of the results of measurements of the impurity-photoconductivity relaxation in p-Si:B under pulsed optical excitation by a narrow-band tunable source of radiation in 'heating' (10-500 V/cm) electric fields is presented. The model takes into account the capture of holes at the ground and lower excited states of boron with optical-phonon emission. It is shown that the dependence of the photoconductivity-relaxation time on the electric-field intensity can be unsteady taking into account these processes. [ABSTRACT FROM AUTHOR]

The relaxation of impurity photoconductivity in p-Si:B crystals subjected to pulsed optical excitation by a narrow-band continuously adjusted source of radiation in the range of 'heating' (10-500 V/cm) electric fields is studied. A variation of dependence of the relaxation time on the electric field E at E > 75 V/cm due to the additional relaxation processes with the emission of an optical phonon is observed. The dependence of the rates of carrier relaxation on the intensity and wavelength of the excitation radiation indicates also that there is a long-lived excited state, which plays the role of a metastable trap level upon the relaxation of charge carriers. [ABSTRACT FROM AUTHOR]

A series of studies of the impurity-photoconductivity relaxation in Si:B is carried out under pulse optical excitation by a narrow-band tunable radiation source in low and 'heating' (10-500 V/cm) electric fields. It is shown that the dependence of the carrier-capture time in a band on the applied electric field is nonmonotonic and, in high fields (>75 V/cm), the capture time decreases with increasing field intensity, which is related to initiating the relaxation processes with optical-phonon emission within the band. The dependence of the relaxation rate for the carriers on the excitation-radiation wavelength is investigated, and a decrease in the carrier-capture time in the band is revealed in the vicinity of the Breit-Wigner-Fano resonances caused by direct capture at an impurity with optical-phonon emission. [ABSTRACT FROM AUTHOR]

The impurity-photoconductivity spectrum is observed for strained quantum wells of the p-InGaAs/GaAs solid solution at T= 4.2 K. In addition to the broad photoconductivity band attributed to the transitions from the acceptor ground state to the continuum of the first size-quantization subband, the spectrum exhibits a peak due to the transitions from the ground state to the excited localized acceptor state, a band corresponding to the transitions to the resonance states associated with the second heavy-hole size-quantization subband, and a narrow photoconductivity peak (Fano resonance) in the spectral range corresponding to the optical-phonon energy. [ABSTRACT FROM AUTHOR]

The energies of odd excited states of shallow acceptors in uniaxially compressed germanium have been calculated as functions of strain and oscillator strengths for transitions from the ground state of an impurity. The calculation allows both a detailed interpretation of the lines previously observed in the photoconductivity and absorption spectra of uniaxially compressed germanium and description of the evolution of these lines with increasing the strain. It has been shown that the photoconductivity of uniaxially compressed germanium depends on the polarization of incident electromagnetic radiation. [ABSTRACT FROM AUTHOR]

Far infrared photoconductivity spectra due to excitation of shallow acceptors in strained multiquantum well Ge/Ge[sub 1-x]Si[sub x] (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 (d[sub Ge≈800 Å), the calculations are shown to qualitatively account for photoconductivity spectra obtained from narrower wells (d[sub Ge]≈200 Å) as well. [ABSTRACT FROM AUTHOR]

In this paper, we report a correction to the model potential of the Ga acceptor in germanium, evidenced by high-magnetic-field photoconductivity measurements. We found that under high magnetic fields the chemical shift of the binding energy of Ga acceptors vanishes, contrary to the results given by the generally accepted theory. To fit our data, we found that the central-cell correction should contain a repulsive part (i.e., it must be bipolar), in contrast to the purely attractive screened point-charge potential widely used in the literature. [ABSTRACT FROM AUTHOR]