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We report on the effect of forward current stress on the low frequency noise in the 4H–SiC rectifier p+-n diodes rated at 20 and 10 kV. The 4H–SiC diodes with 20 kV blocking voltage were the most sensitive to the forward current stress. Even the stress by the current density j=13 A/cm2 for 30 min led to a noticeable increase in the forward voltage drop and changes in the noise spectra. The stress decreased the level of the 1/f noise but led to the appearance of the burst noise. Stress at higher current densities (50 A/cm2) led to the disappearance of the burst noise and to a further increase in the forward voltage drop. Diodes with 10 kV blocking capability were more resistant to the forward current stress. However, they also demonstrated a decrease in the 1/f noise as a result of the 60 min stress at j=100 A/cm2. [ABSTRACT FROM AUTHOR]

The low frequency noise was studied in 4H-SiC metal oxide semiconductor field effect transistors (MOSFETs) in the frequency range from 1 Hz to 100 kHz. 1/f (flicker) noise dominated in output noise over the entire frequency range and for a wide range of drain and gate biases. The dependence of the relative spectral noise density, SI/Id2, on the drain current, Id (at constant drain voltage, Vd), was qualitatively different from typical dependences for n-channel Si MOSFETs. In Si MOSFETs, in strong inversion, SI/Id2 usually decreases as ∼1/Id2 and tends to saturate in the subthreshold region, whereas in SiC MOSFETs under study, SI/Id2∝Id-0.5 for the currents varying from the deep subthreshold regime to the strong inversion. [Similar dependences were often observed in amorphous and polycrystalline thin film transistors (TFTs).] The effective field effect mobility of 3–7 cm2/V s extracted from the measured I-V characteristics is almost as low as that in amorphous Si TFTs. This result might be explained by a high density of localized states near the conduction band in the thin ion implanted silicon carbide layer. The energy dependence of trap density responsible for the noise was extracted for the states located close to the bottom of conduction band. [ABSTRACT FROM AUTHOR]

Presents information on a study which reported on the results of the measurements of low-frequency noise in gallium nitride with high electron mobility. Experimental details; Results and discussion; Conclusions.

The bulk low frequency noise has been investigated in the 4H silicon carbide polytype. In the temperature range of 300-550 K the noise spectral density S is proportional to ƒ[sup -1.5], where ƒ is the measurement frequency. A very low noise level has been observed for the bulk noise. At 300 K, the Hooge constant α is as small as (2-4) × 10[sup -6] at ƒ = 20 Hz and α ≤ 5 × 10[sup -7] at ƒ = 1300 Hz. At T ≥ 600 K, the generation-recombination noise of a local level makes the main contribution into the total low frequency noise. The electron capture cross section σ of this level depends very strongly on temperature. In the temperature range of 620-700 K, the temperature dependence of σ can be expressed as σ ∼ exp(-E[sub 1]/kT), with an activation energy E[sub 1] as high as 2.7 eV. [ABSTRACT FROM AUTHOR]

Schottky diodes with Ni/Au contact to the side of the two dimensional channel in GaN/AlGaN system were fabricated and studied. This kind of lateral heterodimensional diodes demonstrated the ideality factor n=1.2–1.25 and apparent barrier height φb=(0.59–0.63) eV. The noise measurements within the frequencies range from 1 Hz to 50 kHz showed that the diodes demonstrated the superposition of 1/f and generation recombination noise. In spite of extremely small area of lateral Schottky diodes, the amplitude of noise was similar or even smaller than that for AlGaN and GaN Schottky diodes with the regular contact. This makes GaN-based lateral Schottky diodes to be very promising devices for RF and terahertz applications. [ABSTRACT FROM AUTHOR]

The correlation between the noise level 1/f and the degree of mosaic-structure order in gallium nitride epitaxial layers was studied for the first time. Samples with a doping level of Nd – Na≈8×1016cm–3 and a relatively high degree of order were characterized by the Hooge parameter α≈1.5×10–3. This value is unprecedently low for thin GaN epitaxial films. The Hooge parameter was significantly higher for samples with Nd – Na≈1.1×1018cm–3 and a low degree of order despite the fact that α generally decreases with increasing doping level at the same degree of order. Thus, the degree of mosaic-structure order affects not only the optical and electrical characteristics but also the fluctuation parameters of GaN epitaxial layers. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]