A. P. Dmitriev

Plasma wave resonant detection of femtosecond pulsed terahertz radiation by a nanometer field-effect transistor

We report on the room-temperature, resonant detection of femtosecond pulsed terahertz radiation obtained by optical rectification in a ZnTe crystal. The detection was realized using a 250nm gate length GaAs∕AlGaAs heterostructure field-effect transistor. We show that physical mechanism of the detection is related to the plasma waves excited in the transistor channel. The detection is strongly enhanced by increasing the drain current and driving the transistor into the plasma wave instability region. Our results clearly show that plasma wave nanometer transistors can be efficient and fast detectors for terahertz spectroscopic imaging based on the femtosecond pulsed THz sources.

Magnetic field effect on the terahertz emission from nanometer InGaAs/ AlInAs high electron mobility transistors

The influence of the magnetic field on the excitation of plasma waves in InGaAs/AlInAs lattice matched high electron mobility transistors is reported. The threshold source-drain voltage of the excitation of the terahertz emission shifts to higher values under a magnetic field increasing from 0 to 6 T. We show that the main change of the emission threshold in relatively low magnetic fields (smaller than approximately 4 T) is due to the magnetoresistance of the ungated parts of the channel. In higher magnetic fields, the effect of the magnetic field on the gated region of the device becomes important.

Low-frequency noise in GaN'AlGaN heterostructure field-effect transistors at cryogenic temperatures

The low-frequency noise in GaN/AlGaN heterostructure field-effect transistors (HFETs) was studied in the temperature range from 8 to 300 K. A contribution of generation-recombination noise with extremely small activation energy Ea=(1−3) meV was observed at T<50 K. At 70⩽T⩽150 K, the temperature dependence of noise in HFETs with a doped channel exhibited a broad maximum. The position of the maximum was practically independent of the frequency of analysis. The model linking this maximum to the electron tunneling from the channel to the silicon donor level in GaN is discussed.

On the Hooge relation in semiconductors and metals

The expressions describing the low frequency noise caused by defects in semiconductors and metals have been obtained in the framework of a general unified approach for both fluctuations in the number of carriers and their mobility. When fluctuations in the number of carriers are responsible for noise, the spectral noise density is inversely proportional to the carrier concentration squared and to the volume of the sample. The spectral density of the noise caused by mobility fluctuations is inversely proportional to the sample volume, and does not depend either on carrier concentration or on the total number of carriers. In the case when both mechanisms contribute to noise and they are correlated, the dependence of the noise on the number of carriers depends on the relative contribution of these two noise mechanisms. The expressions obtained can be associated with corresponding cases of the 1/f noise. The physical basis and limitations of the Hooge formula are discussed.

Nonlinear screening of pyroelectric films and grains in semiconductor matrix

Many semiconductor electronic and photonic devices use heterostructures, where strain induced and/or spontaneous polarization play a key role. The polarization charges are screened by accumulation and depletion regions, which determine the device properties. This article considers nonlinear screening of the polarization dipole for pyroelectric (or ferroelectric) films and grains in a semiconductor matrix. Our results show that, for a pyroelectric of a finite size in a semiconductor matrix, a nonlinear screening length involved in most relevant cases is different from the conventional depletion length and depends on the geometry of the problem. These results are important for AlN/GaN/InN and SiC based electronic and photonic devices, ferroelectric random access memories, and other pyroelectric and ferroelectric semiconductor materials and devices.

Magnetoresistance of compensated semimetals in confined geometries

Two-component conductors -- e.g., semimetals and narrow-band semiconductors -- often exhibit unusually strong magnetoresistance in a wide temperature range. Suppression of the Hall voltage near charge neutrality in such systems gives rise to a strong quasiparticle drift in the direction perpendicular to the electric current and magnetic field. This drift is responsible for a strong geometrical increase of resistance even in weak magnetic fields. Combining the Boltzmann kinetic equation with sample electrostatics, we develop a microscopic theory of magnetotransport in two and three spatial dimensions. The compensated Hall effect in confined geometry is always accompanied by electron-hole recombination near the sample edges and at large-scale inhomogeneities. As the result, classical edge currents may dominate the resistance in the vicinity of charge compensation. The effect leads to linear magnetoresistance in two dimensions in a broad range of parameters. In three dimensions, the magnetoresistance is normally quadratic in the field, with the linear regime restricted to rectangular samples with magnetic field directed perpendicular to the sample surface.

Ballistic admittance: Periodic variation with frequency

The authors show that both real and imaginary parts of the admittance of short (ballistic or quasiballistic) semiconductor structures are oscillatory functions of the frequency with the period determined by the inverse electron transit time with the Fermi velocity. This oscillatory dependence is caused by the phase difference between the electrons injected from the opposite contacts.

Plasma wave instability in gated collisionless two-dimensional electron gas

We present the solution of the Boltzmann equation for relatively low density gated two-dimensional electron gas where electron–electron collisions are not significant. This solution describes the plasma waves with the same dispersion law as for a high electron sheet density. In both cases, the plasma waves become instable in a short channel field effect transistor with asymmetric boundary conditions at small channel currents (provided that the scattering by phonons and impurity is sufficiently small). Our analysis also shows that for realistic values of the device parameters, the Landau damping is small.

Electron runaway and negative differential mobility in two-dimensional electron gas in elementary semiconductors

We show that two-dimensional electron gas in silicon or germanium should exhibit a negative differential mobility. This effect is caused by the electron runaway since, in contrast to the three-dimensional case, such runaway takes place even for deformation optical polar scattering. As a consequence of the electron runaway, hot electron scatter into the valleys with a larger density of states, which leads to a negative differential mobility.

Generation-recombination noise in forward biased 4H‐SiC p‐n diodes

Low frequency noise has been studied in forward biased 4H‐SiC p+‐n diodes at current densities from 10−4to10A∕cm2. At small current densities j⩽10−3A∕cm2, the spectral noise density SI follows the law SI∝1∕f3∕2. At 10−3A∕cm2 <j<10−2A∕cm2, the generation-recombination (GR) noise predominates. The amplitude of this GR noise nonmonotonically depends on current. At j⩾10−2A∕cm2, the 1∕f (flicker noise) dominates. It has been shown that the recombination time in the space charge region of the p+‐n junction, τR, is about 70ns. This value is approximately one order of magnitude larger than that reported earlier for SiC p‐n structures. A model of GR noise in forward biased p‐n junctions has been proposed. The model links the GR noise with fluctuations of the charge state of a trap in the space charge region.