M. E. Levinshtein

Carrier mobility model for GaN

Abstract Simple analytical approximation has been obtained to describe the temperature and concentration dependencies of the low-field mobility in gallium nitride (GaN) in wide temperature (50⩽ T ⩽1000 K) and concentration (10 14 ⩽ N ⩽10 19 cm −3 ) ranges. The dependence of the temperature T m at which the mobility μ is at a maximum on the doping level is also obtained. Results obtained can be directly used for computer simulation of GaN-based devices.

AlGaN/GaN high electron mobility field effect transistors with low 1/f noise

Low-frequency noise in the frequency region of 20 Hz to 20 kHz is investigated in AlGaN/GaN high electron mobility transistors (HEMTs) grown on SiC substrates. The noise spectra have the form of the 1/f (flicker) noise. The measured Hooge parameter is as low as 0.0001. This value is comparable with Hooge parameter values for commercial GaAs field effect transistors and approximately two orders of magnitude smaller than Hooge parameter value measured for AlGaN/GaN heterostructures grown on sapphire. The level of noise depends on the gate leakage current; the noise is much higher in devices with a high gate leakage current. The small measured values of the Hooge parameter are related to a smaller leakage current and to a better material quality of the devices on SiC substrates and to a high electron sheet density. The low levels of the 1/f noise in the AlGaN/GaN HEMTs on SiC substrates make them suitable for applications in communication systems.

Effect of gate leakage current on noise properties of AlGaN/GaN field effect transistors

The effect of the gate leakage current fluctuations on noise properties of AlGaN/GaN heterostructure field effect transistors (HFETs) has been studied in conventional HFET structures and in AlGaN/GaN metal-oxide-semiconductor heterostructure field effect transistors (MOS-HFETs). The comparison of the noise properties of conventional AlGaN/GaN HFETs and AlGaN/GaN MOS-HFETs fabricated on the same wafer, allowed us to estimate the contribution of the gate current noise to the HFET’s output noise. The effect of the gate current fluctuations on output noise properties of HFETs depends on the level of noise in the AlGaN/GaN HFETs. For the transistors with a relatively high magnitude of the Hooge parameter α∼10−3, even a relatively large leakage current Ig (Ig/Id∼10−3–10−2, where Id is the drain current) does not contribute much to the output noise. In HFETs with a relatively small values of α (α∼10−5–10−4), the contribution of the leakage current to output noise can be significant even at Ig/Id∼10−4–10−3. For s...

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.

Steady-state and transient forward current-voltage characteristics of 4H-silicon carbide 5.5 kV diodes at high and superhigh current densities

Steady-state and transient forward current-voltage I-V characteristics have been measured in 5.5 kV p/sup +/-n-n/sup +/ 4H-SiC rectifier diodes up to a current density j/spl ap/5.5/spl times/10/sup 4/ A/cm/sup 2/. The steady-state data are compared with calculations in the framework of a model, in which the emitter injection coefficient decreases with increasing current density. To compare correctly the experimental and theoretical results, the lifetime of minority carriers for high injection level, /spl tau//sub ph/, has been estimated from transient characteristics. At low injection level, the hole diffusion length L/sub pl/ has been measured by photoresponse technique. For a low-doped n-base, the hole diffusion lengths are L/sub pl//spl ap/2 /spl mu/m and L/sub ph//spl ap/6-10 /spl mu/m at low and high injection levels respectively. Hole lifetimes for low and high injection levels are /spl tau//sub pl//spl ap/15 ns and /spl tau//sub ph//spl ap/140-400 ns. The calculated and experimental results agree well within the wide range of current densities 10 A/cm/sup 2/ 5 kA/cm/sup 2/, the experimental values of residual voltage drop V is lower than the calculated ones. In the range of current densities 5/spl times/10/sup 3/ A/cm/sup 2/ 25 kA/cm/sup 2/, R/sub d/ increases with increasing current density manifesting the contribution of other nonlinear mechanisms to the formation steady-state current-voltage characteristic. The possible role of Auger recombination is also discussed.

Low frequency noise in GaN metal semiconductor and metal oxide semiconductor field effect transistors

The low frequency noise in GaN field effect transistors has been studied as function of drain and gate biases. The noise dependence on the gate bias points out to the bulk origin of the low frequency noise. The Hooge parameter is found to be around 2×10−3 to 3×10−3. Temperature dependence of the noise reveals a weak contribution of generation–recombination noise at elevated temperatures.

Carrier mobility model for simulation of SiC-based electronic devices

Simple analytical approximations are proposed for describing the temperature and concentration dependences of low-field mobility in the main polytypes of silicon carbide (SiC): 6H, 4H and 3C in wide ranges of temperature and concentration. The obtained results can be directly used for the computer simulation of SiC-based devices. Different approaches to the analytical approximation of SiC parameters are critically correlated and analysed.

Temperature dependence of the current gain in power 4H-SiC NPN BJTs

For 1-kV 30-A 4H-SiC epitaxial emitter n-p-n bipolar junction transistors, the dependences of the common-emitter current gain /spl beta//sub CE/ on the collector current I/sub C/ were measured at elevated temperatures. The collector-emitter voltage was fixed (at 100 V) to provide an active operation mode at all collector currents varying in a wide range from 150 mA to 40 A (current densities of 24-6350 A/cm/sup 2/). The maximum current gain was measured to be /spl beta//sub CEmax/=40(I/sub C/=7 A) at room temperature and /spl beta//sub CEmax/=32(I/sub C/=10 A) at 250/spl deg/C. The /spl beta//sub CE/-I/sub C/ dependences were simulated in terms of a model that takes into account the main processes affecting the current gain: 1) recombination in the emitter-base space charge region; 2) surface recombination; 3) crowding of the emitter current; 4) decrease in the emitter-injection coefficient at high-level injection; and 5) ionization of deep acceptors. The minority carrier lifetimes and surface recombination velocity were obtained by means of this simulation.

Factors limiting the current gain in high-voltage 4H-SiC npn-BJTs

Abstract The dependence of the base current gain β on the collector current IC has been measured in high-voltage 4H-SiC bipolar junction transistors at collector current densities jC from 20 to 700 A/cm2. With increasing collector current, the β value grows, reaching a maximum βmax=23 at j C max of about 250 A/cm2 and then decreasing sharply with further increase in current. The peculiarities of this dependence are analyzed in terms of a model taking into account the carrier recombination in the emitter space charge region (SCR), the surface recombination, and the emitter current crowding effect. It is shown that at relatively small jC the recombination in SCR plays a key role in limiting the β magnitudes. The decrease in β at high jC is mainly due to the surface recombination enhanced by the emitter current crowding effect. The effects of surface recombination and recombination in the SCR reduce the maximum current gain almost threefold: from 65 to 23.

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.