H. Maaref

Electrical characterization of (Ni/Au)/Al0.25Ga0.75N/GaN/SiC Schottky barrier diode

In this work we report on the characteristics of a (Ni/Au)/AlGaN/GaN/SiC Schottky barrier diode (SBD). A variety of electrical techniques, such as gate current-voltage (I-V), capacitance-voltage (C-V), and deep level transient spectroscopy (DLTS) measurements have been used to characterize the diode. The behavior study of the series resistance, RS, the ideality factor, n, the effective barrier height, Φb, and the leakage current with the temperature have emphasized an inhomogeneity of the barrier height and a tunneling mechanism assisted by traps in the SBD. Hence, C-V measurements successively sweeping up and down the voltage have demonstrate a hysteresis phenomenon which is more pronounced in the temperature range of 240 to 320 K, with a maximum at ∼300 K. This parasitic effect can be attributed to the presence of traps activated at the same range of temperature in the SBD. Using the DLTS technique, we have detected one hole trap having an activation energy and a capture cross-section of 0.75 eV and 1.0...

Hole injection and transport in ITO/PEDOT/PVK/Al diodes

Abstract The paper reports on the hole injection in Poly(N-vinylcarbazole) (PVK) films from an indium tin oxide (ITO) anode treated with poly(3,4)ethylenedioxythiophene/polystyrenesulphonate (PEDT/PSS) usually called PEDOT. The influence of the deposition conditions of PEDOT on the onset voltage of the diodes is first, investigated and an optimised procedure for the surface treatment of ITO with PEDOT is given. Second, the analysis of the I–V characteristics of various devices with different PVK thickness in a temperature range 100–330 K shows that the hole conduction is bulk limited rather than injection limited. A trap assisted space charge conduction model with an exponential distribution of traps well describes our results. A trap density of 4×1018 cm−3 and a characteristic energy Et−EHOMO=0.15 eV were deduced. A comparison with a conduction model based on trap free material but with electric field dependant mobility is provided.

Improvement of the electron density in the channel of an AlGaAs/GaAs heterojunction by introducing Si δ doping in the quantum well

The electronic subband of δ-doped AlGaAs/GaAs heterostructure has been studied theoretically by the finite differential method. We use an efficient self-consistent analysis to solve simultaneously the Schrodinger and Poisson equations. The results show the possibility to increase the electron density in the channel by the introduction of the silicon δ doping in a quantum well, where the Al concentration is smaller than in the barrier. The effect of the quantum well width is studied on the electron density. To test the validity of our calculation, we have grown, by molecular beam epitaxy, a series of δ-doped AlGaAs/GaAs heterojunctions having various alloy compositions seen by the silicon. If we consider the spreading of the silicon in space during the δ-layer growth, we show that the theoretical model explains well the experimental Hall data for all aluminum concentrations.

Deep‐level analysis of n‐type GaAs1−xPx alloys

Deep‐level transient spectroscopy has been used to study the properties of electron and hole traps present in n‐type GaAs1−xPx alloys and their evolution versus the alloy composition. An electron trap labeled E0 is observed for all values of the alloy composition x, while a second electron trap E1 appears only for 1≳x≥0.81. As for hole traps one (H2) appears for 1≳x≥0.75, while two others, H0 and H1, are detected for x≥0.81 and for 1≳x≥0.81, respectively. Their ionization energies have been determined and the barriers, associated with electron capture, have been measured in order to determine the energetic position of the two electron traps relative to the conduction band.

Excitonic properties of wurtzite InP nanowires grown on silicon substrate

In order to investigate the optical properties of wurtzite (Wz) InP nanowires grown on Si(001) by solid source molecular beam epitaxy with the vapour-liquid-solid method, the growth temperature and V/III pressure ratio have been optimized to remove any zinc-blende insertion. These pure Wz InP nanowires have been investigated by photoluminescence (PL), time-resolved PL and PL excitation. Direct observation of the second and third valence band in Wz InP nanowires using PL spectroscopy at high excitation power have been reported and, from these measurements, a crystal field splitting of 74 meV and a spin-orbit interaction energy of 145 meV were extracted. Based on the study of temperature-dependent optical properties, we have performed an investigation of the thermal escape processes of carriers and the electron-phonon coupling strength.

Wurtzite InP/InAs/InP core–shell nanowires emitting at telecommunication wavelengths on Si substrate

Optical properties of wurtzite InP/InAs/InP core-shell nanowires grown on silicon substrates by solid source molecular beam epitaxy are studied by means of photoluminescence and microphotoluminescence. The growth conditions were optimized to obtain purely wurtzite radial quantum wells emitting in the telecom bands with a radiative lifetime in the 5-7 ns range at 14 K. Optical studies on single nanowires reveal that the polarization is mainly parallel to the growth direction. A 20-fold reduction of the photoluminescence intensity is observed between 14 and 300 K confirming the very good quality of the nanowires.

Evidence of surface states for AlGaN/GaN/SiC HEMTs passivated Si 3 N 4 by CDLTS

In AlGaN/GaN heterostructure field-effect transistors (HEMTs) structures, the surface defects and dislocations may serve as trapping centers and affect the device performance via leakage current and low frequency noise. This work demonstrates the effect of surface passivation on the current-voltage characteristics and we report results of our investigation of the trapping characteristics of Si3N4-passivated AlGaN/GaN HEMTs on SiC substrates using the conductance deep levels transient spectroscopy (CDLTS) technique. From the measured of CDLTS we identified one electron trap had an activation energy of 0.31 eV it has been located in the AlGaN layer and two hole-likes traps H1, H2. It has been pointed out that the two hole-likes traps signals did not originate from changes in hole trap population in the channel, but reflected the changes in the electron population in the surface states of the HEMT access regions.

Optical anisotropy in self-assembled InAs nanostructures grown on GaAs high index substrate

We present a study of the optical properties of InAs self-assembled nanostructures grown by molecular beam epitaxy on GaAs(11N)A substrates (N = 3-5). Photoluminescence (PL) measurements revealed good optical properties of InAs quantum dots (QDs) grown on GaAs(115)A compared to those grown on GaAs(113)A and (114)A orientations substrate. An additional peak localized at 1.39 eV has been shown on PL spectra of both GaAs(114)A and (113)A samples. This peak persists even at lower power density. Supporting on the polarized photoluminescence characterization, we have attributed this additional peak to the quantum strings (QSTs) emission. A theoretical study based on the resolution of the three dimensional Schrödinger equation, using the finite element method, including strain and piezoelectric-field effect was adopted to distinguish the observed photoluminescence emission peaks. The mechanism of QDs and QSTs formation on such a high index GaAs substrates was explained in terms of piezoelectric driven atoms and the equilibrium surfaces at edges.

Self-heating and trapping effects in AlGaN/GaN heterojunction field-effect transistors

This work first attempted to simulate the band edges of AlGaN/GaN high electron mobility transistors (HEMTs) structures with Ga-face polarity at the heterointerface. The spontaneous and piezoelectric-induced polarization fields as well as the effects of temperature on the electron band parameters have been included into the modeling. In a second step, we calculated self-consistently direct-current characteristics of AlGaN/GaN HEMTs without considering any defect. Calculations were made as a function of doping concentration and Al composition. In the paper, the self-heating in AlGaN/GaN HEMTs grown on SiC substrate before and after Si3N4 passivation was also investigated revealing that: (i) power dissipation is induced due to the increase in drain bias, which leads to a temperature rise of the two-dimensional electron gas in the channel, (ii) an enhancement in drain current is achieved after Si3N4 passivation, (iii) the self-heating occurs even in AlGaN/GaN heterostructures after passivation. Including the...

Stoichiometry‐dependent native acceptor and donor levels in Ga‐rich‐n‐type gallium arsenide

By combining photoluminescence and optical deep‐level transient spectroscopy measurements, we have investigated the presence of a native acceptor level H01 situated at 0.32 eV above the valence band, in n‐type Si‐doped liquid‐encapsulated Czochralski GaAs grown in stoichiometric and Ga‐rich conditions. The concentration of H01 decreases when increasing the [Ga]/[As] ratio up to a critical threshold of 1.3. For [Ga]/[As] ratio greater than 1.3, H01 disappears and another acceptor level, H02 (Ev+0.23 eV), is detected. H02 is identified as the double‐acceptor level of the gallium antisite GaAs. Photoluminescence results show the presence of a high‐intensity 1‐eV band which disappears for [Ga]/[As] ratios greater than 1.2. The annihilation of this band is accompanied by the appearance of two emission bands centered at 0.95 and 1.2 eV. The dependence of the free‐carrier concentration on the presence of H01 is interpreted in terms of a complex defect formed by a gallium vacancy and silicon impurity which can be...