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The current voltage characteristics and the low-frequency noise in high voltage 4H-SiC junction barrier Schottky diodes irradiated with high energy (15MeV) protons were studied at different temperatures and irradiation doses Φ from 3 x 1012 cm-2 to 1 x 1014 cm-2. Irradiation led to the increase of the base resistance and the appearance of slow relaxation processes at small, V ≤ 0.2 V, and at rather high, V ≥ 2 V, forward voltages. The characteristic times of these relaxation processes ranged from ~1 µs to 10³s. The exponential part of the current-voltage characteristic was only weakly affected by irradiation. The temperature dependence of the base resistance changed expo-nentially with temperature with activation energy Ea ~ 0.6 eV, indicating that the Z1/2 level plays a dominant role in this process. The temperature increase also led to the increase of the ideality factor from 1.05 at 25 °C to 1.1 at 172 °C. At elevated temperatures and high forward voltages V > 2-4 V, the current voltage characteristics tend to be super-linear. It is concluded that at high voltages, the space charge limited current of majority carriers (electrons) and hole injection from the p-n regions play an important role in the formation of the current voltage characteristic. The frequency dependences of noise spectral density S of proton irradiated Schottky diodes have the unusual form of S ~ 1/f05. [ABSTRACT FROM AUTHOR]

We report on fabrication of MoS2 thin-film transistors (TFTs) and experimental investigations of their high-temperature current-voltage characteristics. The measurements show that MoS2 devices remain functional to temperatures of at least as high as 500 K. The temperature increase results in decreased threshold voltage and mobility. The comparison of the direct current (DC) and pulse measurements shows that the direct current sub-linear and super-linear output characteristics of MoS2 thin-films devices result from the Joule heating and the interplay of the threshold voltage and mobility temperature dependences. At temperatures above 450 K, a kink in the drain current occurs at zero gate voltage irrespective of the threshold voltage value. This intriguing phenomenon, referred to as a "memory step," was attributed to the slow relaxation processes in thin films similar to those in graphene and electron glasses. The fabricated MoS2 thin-film transistors demonstrated stable operation after two months of aging. The obtained results suggest new applications for MoS2 thin-film transistors in extreme-temperature electronics and sensors. [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]

The analysis of experimental data following the McWhorter model for the low frequency noise in amorphous Si thin film transistors (TFTs) with SiNx gate dielectric revealed relatively low density of traps Nt≈1019 (cm3 eV)-1. This value is close to the lower limit ever reported for amorphous and polycrystalline Si TFTs. Trap density only slightly increases with the increase of the gate voltage, i.e., approaching the conduction band edge. [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]

Noise in nanostructures is one of the key problems impeding their applications in electronic devices. We show that the level of 1/f and recombination-generation noise in GaN nanowire field effect transistors can be suppressed by ultraviolet radiation by up to an order of magnitude. This strong suppression of the noise is explained by the illumination changing the occupancy of traps responsible for noise. [ABSTRACT FROM AUTHOR]

We report on the low frequency [1/f and generation-recombination (GR)] noise in InAlAs/InGaAs modulation doped field effect transistors with a 50-nm gate length. The characteristic capture and emission times of the GR noise depended on the gate voltage. Measurements of the noise as a function of the gate voltage showed that the gate leakage current, contacts, and ungated sections of the channel did not contribute to the 1/f noise. The gate voltage dependence of the 1/f noise agreed well with the model of number of carriers fluctuations as a source of the 1/f noise. An effective density of traps responsible for the 1/f noise was found to be Deff≈2.7×1012 cm-2 eV-1. [ABSTRACT FROM AUTHOR]

Light intensity low-frequency noise was studied in green GaInN/GaN quantum well light emitting diodes. The light intensity noise was measured as a function of wavelength within the light emitting diode spectral emission line. The spectral noise density is found to increase with decreasing wavelength. Comparing the wavelength-resolved noise with the total light noise, we found that the emission intensity fluctuates synchronously across the entire linewidth. The source of this noise can be ascribed to nonradiative recombination centers. [ABSTRACT FROM AUTHOR]

Low frequency noise of current and light intensity of ultraviolet light emitting diodes (LED) with wavelength from 265 to 340 nm are the superposition of the 1/f and generation-recombination noise. The dependence of generation-recombination noise on the LED current has a maximum caused by a relatively shallow trap level in the quantum well. The upper bound of this trap level concentration is estimated to be Nt=7×1015 cm-3. The relative spectral noise density of the light intensity fluctuations decreased with an increase of the LED forward current. At high currents, the difference in the noise level for LEDs with different wavelength is small and is of the same order of magnitude or even smaller than for visible LEDs. [ABSTRACT FROM AUTHOR]

Low-frequency fluctuations of current and light intensity were measured for different types of ultraviolet (UV) light-emitting diodes (LEDs) with wavelengths from 280 to 375 nm. These UV LEDs are suitable for studying steady-state and time-varying UV fluorescences of biological materials. The correlation coefficient between the current and light intensity fluctuations varies with the LED current and load resistance. This dependence is explained in terms of contributions to the 1/f noise from the active region and from the LED series resistance. The noise level could be reduced by operating the UV LEDs at a certain optimum current level and with large external series resistance. [ABSTRACT FROM AUTHOR]

We propose a model of the 1/f noise in GaN/AlGaN heterojunction field-effect transistors that links the 1/f noise to the tunneling from the two-dimensional electron gas in the device channel into the tail states near the conduction band of the GaN layer. The model predicts a fairly weak temperature dependence of the 1/f noise in the temperature interval from 50 to 600 K with the value of the Hooge parameter α within the range of 10-3–10-5. Both these predictions are in agreement with experimental data. [ABSTRACT FROM AUTHOR]

Experimental data on the low-frequency noise in GaN/AlGaN heterostructure field effect transistors show that the spectral noise density of the drain current fluctuations, S[SUBI], close to the saturation voltage increases faster than the square of the drain voltage V[SUBd]. At drain voltages higher than the saturation voltage, S[SUBI] decreases with a further increase in drain voltage. A model of noise behavior below saturation based on the tunneling mechanism of noise is in a good agreement with the data measured. [ABSTRACT FROM AUTHOR]

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 E[SUBa]= (1 - 3) meV was observed at T<50 K. At 70&les;T&les;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. [ABSTRACT FROM AUTHOR]

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 2x10[sup -3] to 3x10[sup -3]. Temperature dependence of the noise reveals a weak contribution of generation-recombination noise at elevated temperatures. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present a model of low frequency noise for degenerate semiconductors. The model links the 1/f noise to tail states near the band edges with a capture cross section that is strongly energy dependent. It predicts that the low frequency noise is not very sensitive to a particular shape of the density of the tail states and that, in degenerate semiconductors, the level of noise should decrease with an increase in the degree of degeneracy. The model also explains the dependence of the noise level on the band-to-band illumination, in qualitative agreement with experimental data. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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[sup -3], even a relatively large leakage current I[sub g] (I[sub g]/I[sub d]∼10[sup -3]-10[sup -2], where I[sub d] is the drain current) does not contribute much to the output noise. In HFETs with a relatively small values of α (α∼10[sup -5]-10[sup -4]), the contribution of the leakage current to output noise can be significant even at I[sub g]/I[sub d]∼10[sup -4]-10[sup -3]. For such transistors, a very rapid increase of the 1/f noise with gate bias was observed. The differences in the noise behavior can be linked to the material quality of the AlGaN and GaN layers in different types of HFETs. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on the flicker noise in pentacene organic thin film transistors (TFT) of different designs. Effect of the TFT design on the noise level and dependence on the gate and drain-source biases; Extracted Hooge parameter alpha; Higher noise level of the bottom source and drain contacts TFT.

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]