Ultrahigh frequency components in the hot electron photomagnetoelectric response of strongly photoexcited narrow-gap semiconductors

A photomagnetoelectric effect has been investigated in semiconductors InAs and CdxHg1-xTe (x=0.2 and 0.26) excited by Q-switched neodymium-YAG laser. The photomagnetoelectric signal undergos double-sign-inversion when the intensity of the exciting light pulses exceeds a critical value Ic=5×1024 photons/(cm2 s) for InAs and (1-4)×1024 photons/(cm2 s) for CdxHg1-xTe samples. It is shown that a frequency spectrum of photomagnetoelectric response is broadened significantly in the region of high frequencies. In general three frequency bands were distinguished. From this investigation it follows that using laser pulses of a duration topt∼1-10 ps the photomagnetoelectric signal in the terahertz range may be generated

High-field electron transport in doped ZnO

Current-voltage characteristics have been measured for ZnO:Ga and Zn:Sb epitaxial layers with electron densities ranging from 1.4x10(17) cm(-3) to 1.1 x 10(20) cm(-3). Two-terminal samples with coplanar electrodes demonstrate virtually ohmic behavior until thermal effects come into play. Soft damage of the samples takes place at high currents. The threshold power (per electron) for the damage is nearly inversely proportional to the electron density over a wide range of electron densities. Pulsed voltage is applied in order to minimize the thermal effects, and thus an average electric field of 150 kV cm(-1) is reached in some samples subjected to 2 ns voltage pulses. The results are treated in terms of electron drift velocity estimated from the data on current and electron density under the assumption of uniform electric field. The highest velocity of similar to 1.5 x 10(7) cm s(-1) is found at an electric field of similar to 100 kV cm(-1) for the sample with an electron density of 1.4 x 10(17) cm(-3). The nonohmic behavior due to hot-electron effects is weak, and the dependence of the electron drift velocity on the doping resembles the variation of mobility

Electron drift velocity in lattice-matched AlInN/AlN/GaN channel at high electric fields

Hot-electron transport was probed by nanosecond-pulsed measurements for a nominally undoped two-dimensional channel confined in a nearly lattice-matched Al0.82In0.18N/AlN/GaN structure at room temperature. The electric field was applied parallel to the interface, the pulsed technique enabled minimization of Joule heating. No current saturation was reached at fields up to 180 kV/cm. The effect of the channel length on the current is considered. The electron drift velocity is deduced under the assumption of uniform electric field and field-independent electron density. The highest estimated drift velocity reaches ∼3.2×107 cm/s when the AlN spacer thickness is 1 nm. At high fields, a weak (if any) dependence of the drift velocity on the spacer thickness is found in the range from 1 to 2 nm. The measured drift velocity is low for heterostructures with thinner spacers (0.3 nm)

Spectra of Wideband Dipole Radiation Induced by the Photomagnetoelectric Response in Narrow Gap Semiconductors

The frequency spectra of sign inverted photomagnetoelectric responses in narrow gap semiconductors InSb, InAs, and $Cd_{0.2}Hg_{0.8}Te$, excited by nanosecond laser light pulses, were used for calculation of induced electromagnetic radiation frequency spectra in dipole approximation. The parallelepiped shape sample was considered as capacitor-like point dipole. The known Fourier transform property was used in calculations. Features of double sign inverted signals formation and its spectra are considered and compared with experimental results. The radiation of pulses, having spectra in terahertz range when excited by picosecond laser pulse from capacitor-like radiators that demonstrate double sign inverted photoresponses, is expected

The Electric Field and Temperature Dependence of Conductance of Two-Dimensional Electron Gas in AlGaN/AlN/GaN

The two-dimensional gas in AlGaN/AlN/GaN heterostucture with a very thin (0.6 nm) AlN spacer was investigated by conductivity relaxation measurements in 86-300 K temperature range. The results show the presence of two exponential relaxation processes characterized by different characteristic time constants. Parameters of the fast and slow components of the processes differently depend on the electric field and temperature. The fast process is attributed to influence of the electric field on the barrier formed by the spacer, while the slow process is attributed to the hot-electron capture out of the channel followed by electron thermal release

Hot-Phonon Decided Carrier Velocity in AlInN/GaN Based Two-Dimensional Channels

Nanosecond-pulsed measurements of hot-electron transport were performed for a nominally undoped two-dimensional channel confined in a slightly strained $Al_{0.8}In_{0.2}N$/AlN/GaN and nearly lattice matched $Al_{0.84}In_{0.16}N$/AlN/GaN heterostructures at room temperature. No current saturation is reached because we minimized the effect of the Joule heating. The electron drift velocity is deduced under assumption of uniform electric field and field-independent electron density. The estimated drift velocity ≈ 1.5 × $10^7$ cm/s at 140 kV/cm bodes well with the value of hot-phonon lifetime exceeding 0.1 ps

Ultrahigh Frequency Components in the Hot Electron Photomagnetoelectric Response of Strongly Photoexcited Narrow-Gap Semiconductors

A photomagnetoelectric effect has been investigated in semiconductors InAs and CdxHg1-xTe (x=0.2 and 0.26) excited by Q-switched neodymium-YAG laser. The photomagnetoelectric signal undergos double-sign-inversion when the intensity of the exciting light pulses exceeds a critical value Ic=5×1024 photons/(cm2 s) for InAs and (1-4)×1024 photons/(cm2 s) for CdxHg1-xTe samples. It is shown that a frequency spectrum of photomagnetoelectric response is broadened significantly in the region of high frequencies. In general three frequency bands were distinguished. From this investigation it follows that using laser pulses of a duration topt∼1-10 ps the photomagnetoelectric signal in the terahertz range may be generated

Applicable Damage of High-TcT_{c} YbaCuO Superconducting Tapes by Current and Laser Pulses

Damage and irreversible damage of YBaCuO tapes with high density current after switching from superconducting to normal state are investigated. Quasi-homogeneous current distribution across the tape in superconducting state can cause perfect tape damage or irreversible damage when current is slightly above critical value. The model of the tape heating during the optically initiated switching from superconducting to normal state is proposed. Analysis of causes inducing damage shows necessity to consider $0.5T_{m}$ damage criterion because of strong current influence on the damage processes. Possible damage mechanisms are described and crack tips motion simultaneously with switching from superconducting to normal state is considered. Application of optically illuminated YBaCuO tapes with nanosecond duration current pulses on the base of the described mechanisms is proposed

Measurements of volt-ampere characteristics of wide gap semiconductor devices in nanosecond time scale

Measurements of volt-ampere characteristics of a nitride and carbide wide gap semiconductor devices using power electrical pulses of nanosecond duration eliminate Joule heating of the devices. However the devices operating at high electric field and having structures of nanometer size may be damaged by short electrical pulses due to consequence of overheating which begins at submicron inhomogeneities during the pulse rise time