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High electron mobility transistors built using $$\hbox {In}_{0.52}\hbox {Al}_{0.48}\hbox {As}$$ / $$\hbox {In}_{0.53}\hbox {Ga}_{0.47}\hbox {As}$$ on InP substrates are currently being investigated for numerous applications due to their favorable performance for microwave, optical and digital applications. We present a detailed and comprehensive study of steady-state and transient electronic transport in $$\hbox {In}_{0.52}\hbox {Al}_{0.48}\hbox {As}$$ with a three-valley model using the semi-classical ensemble Monte Carlo method including all important scattering mechanisms. Electronic transport parameters such as drift velocity, valley occupation, average electron energy, ionization coefficient and generation rate, electron effective mass, diffusion coefficient, energy and momentum relaxation time are extracted rigorously from the simulations. Using these, we present a detailed characterization of the transient electronic transport showing the variation of drift velocity with distance and time. We further estimate the optimal cut-off frequencies for various device lengths via the velocity overshoot effect. Our analysis shows that transient effects are significant for device lengths shorter than 700 nm and should be taken into account for optimal device designs. As a critical example at length scales of around 100 nm, we obtain a significant improvement in the cut-off frequency from 261 GHz to 663 GHz with the inclusion of transient effects. The field dependence of all extracted parameters done here can prove to be highly useful for further device analysis and design.

In this paper, we introduce three new structures of a cylindrical gate-all-around nanowire (NW) field-effect transistor (FET) to achieve negative differential resistance (NDR) and negative transconductance (NTC) behaviors. In the first structure, only one metal is implanted in the channel near the drain of the dual-material cylindrical gate-all-around NWFET based on the energy band profile modulation to obtain the NDR behavior. To achieve NTC behavior, another metal is implanted in the channel near the source; therefore, the second structure has both the NDR and NTC behaviors. In the final structure, the use of a triple-metal gate is proposed to improve the peak-to-valley current ratio. The NTC behavior occurs when the increase in VGS creates a positive lateral electric field in the channel, which causes the potential barrier tunneling (PBT) to decrease. The cause of the positive electric field formation is the cavity in the channel’s potential barrier due to implanted metals. Furthermore, by increasing VDS, the high electron scattering caused by the high electric field at the beginning of the drain region is increased and causes the electron drift velocity and IDS to decrease. Consequently, the NDR behavior is achieved. The structures are carefully simulated using numerical simulation based on non-local tunneling, and also the transfer characteristics (IDS − VGS) and the output characteristics (IDS − VDS) are attentively analyzed and examined.

This paper compares the electronic transport proprieties of two materials, InP and InAs0.3P0.7, in order to present the advantageous characteristics of InAs0.3P0.7 and which in turn leads to inventing of a first substrate derived from InP. This comparative study is performed by using Monte Carlo methods at room temperature and includes the acoustic, polar and inter-valley scattering mechanisms, as well as the energy and drift velocity of charge carriers. The obtained results show that InAs0.3P0.7 presents better behavior in terms of charge carrier energy and drift velocity compared to InP, due to its low set energy describing the band energy of InAs0.3P0.7, as well as high atomic density. On the other hand, the registered energy saturation for charges carriers in the case of InAs0.3P0.7 is reached quickly and under lower applied electric fields compared to InP, due to its high rate of scattering, making InAs0.3P0.7 better than InP for use in high-frequency and low-power operation applications.

WOS: 000371167600002, Molecular beam epitaxy-grown InxGa1-xN/GaN samples with indium fraction x ranging between 0.44 and 0.784 were studied by pulsed current-voltage (I-V) measurements at 1.7 K. The drift velocity, electron mobility, and electric-field-dependent power loss per electron were determined from analysis of the data. The drift velocity increased linearly while the electron mobility remained constant with increasing electric field. Power balance equations were used to obtain the power loss per electron as a function of the applied electric field in the range of 0 kV cm(-1) to 230 kV cm(-1). The results showed that the power loss per electron increased in the x range of 0.44 to 0.66, then slowly decreased in the x range of 0.66 to 0.784. The results obtained for the dependence of the power loss on the electron temperature are compared with current theoretical models for the power loss in two-dimensional (2D) semiconductors, which include both piezoelectric and deformation potential scattering. For all samples, the energy relaxation of electrons is dominated by acoustic phonon emission via piezoelectric interaction., Anadolu University Scientific Research Projects Commission [1306F137, 1404F170], This study was supported by Anadolu University Scientific Research Projects Commission under Grant Nos. 1306F137 and 1404F170.

The impulse response time has been measured as a function of reverse bias, gain, and temperature in backside-illuminated short-wave infrared HgCdTe avalanche photodiodes (APDs) with variable junction geometry. The APD geometry was altered using HgCdTe substrates of variable thickness and by variation of device fabrication parameters. This approach allowed study of the drift–diffusion dynamics of the electrons before entering the junction and the electron and hole dynamics during the junction transition in APDs with different carrier collection distances and junction widths. The response time was typically limited by a double exponential decay, which is attributed to contributions from the impedance mismatch between the interconnection circuit and the 50-Ω radiofrequency probe, and a delayed diffusion response from carriers generated far from the junction. These contributions limited the maximum bandwidth of the diodes to about 600 MHz, independently of gain and temperature. The hot carrier velocities are estimated by fitting the measured response with numerical calculations, taking into account contributions from a direct drift–multiplication response and a delayed diffusion response. This analysis shows that the hot carrier dynamics is close to independent of temperature and that the electron drift velocity saturates at the gain onset to a value of 1 × 107 cm/s, decreasing upon a further increase of the electric field E to a value of about 3 × 106 cm/s at E = 100 kV/cm. The hole velocity shows a slow variation from 3 × 106 cm/s at low electric fields to 1.5 × 106 cm/s at high electric fields.

A combined study of the avalanche gain characteristics of HgCdTe electron-avalanche photodiodes (e-APDs) and of the minority electron properties in the p-type absorber using Shockley–Haynes (SH) measurements is presented for various Cd compositions x Cd. Ideal gain performance associated with a low excess noise factor F = 1.2 have been measured at T = 80 K down to cutoff wavelengths of λ c = 2.9 μm. The observation of both a record high, exponentially increasing gain of M = 600 in short-wave e-APDs and a low excess noise factor proved that the exclusive electron multiplication is stable down to x Cd = 0.4. Zero-flux measurements at 80 K confirmed that the dark current tends to decrease at constant gain as x Cd increases. Measurements using a readout integrated circuit allowed us to establish a new record in sensitivity for APDs: I eq_in = 2 aA, corresponding to 12 e/s at gain of M = 24 in an e-APD with λ c = 2.9 μm. SH measurements enabled direct estimation of the electron diffusion coefficient, drift velocity, and lifetime in the p-type absorber of the e-APDs as a function of electric field at temperatures between 80 K and 200 K. Measurements at 80 K yielded lifetimes consistent with the values expected for the nominal doping of the samples. The low-field electron drift mobility, estimated from the drift velocity, was found to be a factor of 0.4 to 0.5 lower than the mobility in n-type material with the same composition. In mid-wave (MW) infrared samples with λ c = 5.3 μm, the mobility was observed to be μ ep = 15 kcm2/Vs to 20 kcm2/Vs, being less than μ en ≈ 40 kcm2/Vs to 50 kcm2/Vs. The reduction in mobility can, in part, be attributed to scattering by ionized acceptors and heavy holes. The diffusion mobility, estimated from the diffusion coefficient, was systematically higher than the drift mobility, indicating diffusion of hot electrons with a temperature higher than that of the lattice. The saturation velocity, v sat_ep = 2 × 106 cm/s to 6 × 106 cm/s, did not correlate with the Cd composition in the samples. The measured saturation velocities made it possible to estimate the timing jitter in p-type absorbers with a built-in electric field. Jitter below 100 ps was estimated for SW and MW APDs with absorbing layer thicknesses up to 4 μm.

Electron and hole transport in wurtzite phase ZnO is studied using an ensemble full band Monte Carlo method. The model includes an accurate description of the electronic structure obtained with the nonlocal pseudopotential method and numerically calculated impact ionization transition rates based on a wavevector-dependent dielectric function. Results of transport simulations at both low and high electric fields are presented. It is found that the low field electron mobility is close to 300 cm 2 V -1 s -1 at room temperature, and the peak electron drift velocity is 2.2 × 10 7 cm/s at a field of 275 kV/cm. The determination of the ionization coefficients is affected by some uncertainties due to the incomplete knowledge of the high energy phonon scattering rates. Nevertheless, the present calculations of the ionization coefficients provide a reasonably accurate estimate of the impact ionization process.

Anomalous diffusion profiles of Ag in single crystalline CdTe were observed using the radiotracer 111Ag. The diffusion anneals were performed at 800 K under Cd or Te vapor and in vacuum with low Ag concentrations. The measured Ag profiles directly reflect the distribution of the self-interstitials and vacancies of the Cd sublattice and are the result of chemical self-diffusion which describes the variation of the deviation from stoichiometry of the binary crystal as a function of depth and time. It turned out that the spread of the Ag dopant essentially is determined by the drift of the charged defects within the electric field caused by the distribution of the extrinsic and intrinsic defects.

High field-dependent electron transport characteristics in 4H-SiC were measured successfully using a nanosecond-pulsed technique. It should be noted that the velocity-field characteristics of SiC are different from GaAs in that SiC does not have velocity overshooting behavior. Without the overshooting behavior, the current density of SiC metal-semiconductor field-effect transistors (MESFETs) is restricted fundamentally by the low drift velocity in the low-field, parasitic regions. These parasitic regions not only limit the current density but also are responsible for a significant shift of the threshold voltage.

We studied the sensitivity of the steady-state electron transport in GaN to variations in the important material parameters related to the band structure. We found (a) that an increase in the lowest conduction-band-valley effective mass leads to a lowering and broadening of the peak in the velocity-field characteristic, as well as to an increase in the field at which the peak occurs; (b) that increases in the upper conduction-band-valley effective masses dramatically decrease the saturation drift velocity, with very little other effect; (c) that increased nonparabolicity of the lowest conduction-band valley leads to a broadening and shifting to higher electric fields of the peak in the velocity-field characteristic; (d) that increases in the intervalley energy separation lead to moderate increases in the peak drift velocity; and (e) that increases in the degeneracy of the upper conduction-band valleys leads to a moderate decrease in the saturation drift velocity.

Depletion and hillock formation were examined in-situ in a scanning electron microscope (SEM) during electromigration of bamboo Al interconnect segments. Hillocks formed directly at the anode ends of the segments by epitaxial addition of Al at the bottom Al/TiN interface. Depletion occurred nonuniformly from the cathode end and stopped once the distance between the leading void and the hillock reached the critical length for electromigration at the given current density. A modified equation for the drift velocity is proposed, which includes the effect of nonuniform depletion and predicts that interconnects with nonuniform depletion are more reliable than those with uniform depletion.

We report on the temporal and the frequency response of both metal-semiconductor-metal (MSM) and p-i-n ultraviolet photodetectors fabricated on single-crystal GaN. The best MSM devices show a fast 10–90% rise-time of ∼28 psec under comparatively low ultraviolet excitation of ∼0.1 W/cm2 averagerirradiance. The fast-Fourier transform (FFT) of the pulse response data indicates a bandwidth, f3dB, of ∼3.8 GHz at a reverse bias of 25 V. This agrees well with the direct frequency response measurement value of ∼3.5 GHz. For the p-i-n devices, we measured a rise-time of ∼43 psec at 15 V reverse bias for a 60 µm diameter mesa with 1 µm thick intrinsic region. The FFT of the p-i-n pulse response obtains f3dB ≈1.4 GHz. Analysis in terms of reverse bias and geometric scaling indicates that the MSM photodetectors are transit-time limited. The p-i-n devices also show evidence of transit-time limited effects based on trends with respect to reverse bias and intrinsic region thickness. However, our larger area p-i-n devices show clear evidence of RC-limited behavior. Modeling of the temporal behavior indicates that a slow component in the time and frequency response data is a consequence of the hole drift velocity. We have also found preliminary evidence of microplasmic effects in the p-i-n devices.

InAs heterojunction bipolar transistors (HBTs) are promising candidates for low power and high frequency (THz) device applications due to their small bandgap, high electron mobility, and high saturation drift velocity. However, doping limits such as the trade-off between desired low intentional n-type concentrations and unintentional doping, and the realization of high p-type concentrations, must still be considered in device design and synthesis. In order to observe the impact of intentional and unintentional n-type doping on diode electrical properties, InAs-based homojunction diodes have been grown on InAs substrates by solid-source molecular beam epitaxy (SSMBE) and were subsequently fabricated and characterized.

At low temperatures, electromigration in polycrystalline Al thin-film conductors has been considered to occur predominantly along grain boundaries. As conductor widths decrease below the average grain size, however, other transport mechanisms will become important. Here we examine electromigration transport mechanisms in narrow AlSiCu conductors in the temperature range 190 to 290°C using the stripe drift technique. For conductors with widths between 0.9 and 2.75 μm both the absolute values of the drift velocity and the activation energy for drift are consistent with a lattice diffusion mechanism. Over this linewidth range the Al microstructure ranges from near-bamboo to approximately 20 μm long polycrystalline segments. The independence of the drift data from the linewidth shows that steady state transport is controlled by the bamboo regions of the conductors, which results from the slower rate of diffusion of Al through the lattice compared to along grain boundaries.

The electromigration lifetime of integrated circuit metallisation is commonly found to increase if the metallisation is covered with a passivation layer such as glass. We have investigated the electromigration behaviour of aluminium conductor stripes under different thicknesses of oxide passivation formed by anodisation. The ionic drift velocity of anodised stripes was measured using the Blech-Kinsbron edge displacement technique (Thin Solid Films 25 327 (1975)) and it was found that the drift velocity decreased with increasing anodisation thickness. Stripes tested with a reversed current drifted backwards with an initial velocity which exceeded the original forward velocity. These results are related to a change in the self-diffusivity of aluminium as a result of high compressive stresses imposed by the anodised layer, and the distribution of stress in a drifting stripe is discussed. A general conclusion is that passivation layers can support compressive stresses sufficient to retard mechanical failure processes in metallisation in two distinct ways, either by raising the threshold stress for the nucleation of damage such as hillocks or whiskers, or by reducing the diffusivity in the metallisation.

The static electron velocity-field characteristics for n-In0.53Gan0.47AS have been measured at temperatures from 95 K to 300 K over a range of electric field strengths from about 10 kV/cm to beyond 100 kV/cm. The velocity decreases monotonically with increasing electric field at all temperatures over the range of field strengths investigated. The electron velocity-field curves for In0.53Ga0.47As exhibit a larger peak-to-valley ratio, lower high-field velocity, and a smaller high-field temperature dependence than those for GaAs measured using the same experimental technique.