Nonlinear fir magneto-photoconductivity on quasi-bound Coulomb states of light holes in high purity p-Ge

Jungwirt, G.; Kropf, R.; Prettl, Wilhelm

doi:10.1007/bf01008902

Cited by 2 publications

(2 citation statements)

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“…The appearance of high-power pulsed FIR and SBM lasers ͑first of the TEA CO 2 -pumped, molecular-gas type 1,2 and, subsequently, of free-electron lasers 3,4 and p-Ge semiconductor devices [5][6][7][8][9][10] ͒ capable of delivering nanosecond pulses of high intensity, up to a few MW, has opened up totally new vistas in investigation of semiconductors in the FIR range and provided a basis for development of far-infrared spectroscopy of semiconductors at high excitation levels, which was first made use of at the Ioffe Physicotechnical Institute. 11 In this frequency range, the high radiation intensity gives rise to a variety of nonlinear phenomena in semiconductors and semiconductor structures ͑see, e.g., review 12 ͒, such as, for example, multiphoton absorption, [13][14][15][16][17][18][19] absorption saturation ͑bleaching͒, [20][21][22][23][24][25][26][27][28][29][30] nonlinear cyclotron resonance, 31,32 impact ionization, 33,34 nonlinear photoacoustic spectroscopy, 35 high-harmonic generation, 36,37 and the high-frequency Stark effect, 38 whose characteristics differ substantially from their counterparts observed both in the visible and infrared ranges and in the range extending from microwaves to dc electric fields. The reason for this lies in that the FIR-SBM range is actually a domain where the interaction in the electronphoton system undergoes a transition from the quantum to classical limit, thus creating a unique possibility to study the same physical phenomenon in conditions where by...…”

Section: Introductionmentioning

confidence: 99%

Deep impurity-center ionization by far-infrared radiation

1997

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An analysis is made of the ionization of deep impurity centers by high-intensity far-infrared and submillimeter-wavelength radiation, with photon energies tens of times lower than the impurity ionization energy. Within a broad range of intensities and wavelengths, terahertz electric fields of the exciting radiation act as a dc field. Under these conditions, deep-center ionization can be described as multiphonon-assisted tunneling, in which carrier emission is accompanied by defect tunneling in configuration space and electron tunneling in the electric field. The field dependence of the ionization probability permits one to determine the defect tunneling times and the character of the defect adiabatic potentials. The ionization probability deviates from the field dependence e(E)ϰexp(E 2 /E c 2) ͑where E is the wave field, and E c is a characteristic field͒ corresponding to multiphonon-assisted tunneling ionization in relatively low fields, where the defects are ionized through the Poole-Frenkel effect, and in very strong fields, where the ionization is produced by direct tunneling without thermal activation. The effects resulting from the high radiation frequency are considered and it is shown that, at low temperatures, they become dominant.

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Section: Introductionmentioning

confidence: 99%

Deep impurity-center ionization by far-infrared radiation

1997

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“…The generation rate is increased by impact ionization of the optically populated final state [5]. As free carriers are captured in high excited states and cascade down to the ground state by emission of phonons, impact ionization of impurities in excited states generally lowers the recombination rate and thus increases the life time in the conduction band [6].…”

Section: (T)mentioning

confidence: 99%

FIR photoconductivity at filamentary current flow in n-GaAs in a magnetic field

Голубев

Prettl

1991

Solid State Communications

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A large number of spectral structures are observed by far infrared magneto-photoconductivity in n-GaAs at 4.2K biased above impurity breakdown in a regime where current flow is filamentary. Phase changes are found in the center of the ls-2p+l line and new structures are observed which shift to higher magnetic fields with increasing bias voltage. The large strength and the intensity dependence of the photosignals indicate that the observed phenomena are due to self-organizing effects of the filament. Small variations of the electron population by infrared irradiation may cause substantial rearrangements of the spatial current distribution.At low temperatures the autocatalytic process of impact ionization of shallow impurities in high-purity semiconductors leads to highly nonlinear current-voltage characteristics. At a critical breakdown voltage the impact ionization rate of impurities exceeds the capture rate of free carriers at low concentrations yielding a rapid increase of the current at a practically constant voltage across the sample. At breakdown a strongly ionized channel is formed in the sample constituting a current filament which carries the total current. The increase of the current is then caused by a lateral growth of the current filament.Here we report on peculiarities which were found in the photoconductivity of n-GaAs when the sample was biased in the nonlinear regime of the current-voltage characteristic and subjected to an external magnetic field. Enhancement of resonant structures in magneto-photoconductivity spectra due to free carrier multiplication, resonant negative photoconductivity and even structures which cannot be attributed to optical impurity transitions are observed. The phenomena may qualitatively be understood from the spatial structure of the filamentary current flow in n-GaAs [1] and the Hall voltage which develops across the filament in a magnetic field leading to different free carrier multiplication rates at opposite edges of the filament [2].The measurements were carried out on n-GaAs epitaxial layers prepared on semiinsulating substrates by vapour phase epitaxy. Results are presented for a sample of ND -NA = 2.7 • 1014 cm -s effective donor concentration, NA/ND ----0.35 compensation ratio and 14 #m thickness. The size of the sample was 3 x 5 mm2; ohmic Indium point contacts were alloyed on opposite edges along the shorter side. The sample was immersed 1035 in liquid helium at 4.2 K in the center of a superconducting solenoid. As sketched in the insert of Fig. 2, the epitaxial layer showed the typical nonlinear currentvoltage relation with three characteristic regimes: (1) high-ohmic pre-breakdown current flow, (2) transition regime from high-resistive to low-resistive behaviour and (3) low-ohmic stable post-breakdown regime. The photoconductive response in Faraday configuration was measured for various biasing conditions as a function of the magnetic field strength up to 6 T using a standard load resistor circuit and lock-in technique. As radiation sources an H20 and an HCN...

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Nonlinear fir magneto-photoconductivity on quasi-bound Coulomb states of light holes in high purity p-Ge

Cited by 2 publications

References 17 publications

Deep impurity-center ionization by far-infrared radiation

Deep impurity-center ionization by far-infrared radiation

FIR photoconductivity at filamentary current flow in n-GaAs in a magnetic field

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