PACS 73.40.Gk, 81.05.Ea, 81.15.Hi, 85.30.Mn GaN/AlGaN double barrier resonant tunnelling structures grown by molecular beam epitaxy on GaN templates have been studied. Peaks in the I(V) characteristics are observed, which are similar to resonant peaks seen in conventional III-V based devices. However, the behaviour of the peaks in I(V) depend upon the previous charge-state of the device produced by electrical bias. Current instabilities are also observed at low voltages. The possible origin of the peaks in the I(V) at room temperature and 4 K is discussed. . Doublebarrier RTDs are the basic benchmark for quantum tunnelling devices. They have been made in a variety of materials systems, including AlGaAs, Si/Ge, and InAs/GaSb. If RTDs could be produced in the group III-Nitrides, a number of novel possibilities exist for development and exploitation. Due to the large band offsets, it should be possible to observe quantum behaviour at much higher temperatures than in other III-Vs. However for group III-Nitride tunnel barrier devices, two problems remain: the structural quality of the heterojunctions and the scattering by impurities due to the high background doping level. Both can destroy the translational invariance that leads to the conservation of electron momentum necessary for successful operation of RTDs.Conventional III-V RTDs are grown mainly by molecular beam epitaxy (MBE). For the group III-Nitrides, because no bulk GaN substrates were available, all structures were initially grown by hetero-epitaxy on sapphire or SiC substrates. Now, due to the availability of GaN templates, grown by hydride vapour phase epitaxy (HVPE) or metal organic vapour phase epitaxy (MOVPE), the structural and optical properties of MBE grown GaN films have been dramatically improved.The effective mass for GaN is about three times larger than for GaAs, so the quantum wells (QWs) in RTDs need to be thinner than in the arsenides [6]. For the tunnel barriers, the transmission coefficient (T) is given by T ~ exp (-2kb), where k = [2m*(V -E)]
Pulsed Laser Deposition is a commonly used non-equilibrium physical deposition technique for the growth of complex oxide thin films. A wide range of parameters is known to influence the properties of the used samples and thin films, especially the oxygen-vacancy concentration. One parameter has up to this point been neglected due to the challenges of separating its influence from the influence of the impinging species during growth: the UV-radiation of the plasma plume. We here present experiments enabled by a specially designed holder to allow a separation of these two influences. The influence of the UV-irradiation during pulsed laser deposition on the formation of oxygen-vacancies is investigated for the perovskite model material SrTiO3. The carrier concentration of UV-irradiated samples is nearly constant with depth and time. By contrast samples not exposed to the radiation of the plume show a depth dependence and a decrease in concentration over time. We reveal an increase in Ti-vacancy–oxygen-vacancy-complexes for UV irradiated samples, consistent with the different carrier concentrations. We find a UV enhanced oxygen-vacancy incorporation rate as responsible mechanism. We provide a complete picture of another influence parameter to be considered during pulsed laser depositions and unravel the mechanism behind persistent-photo-conductivity in SrTiO3.
PACS 72. 70.+m, 73.40.Kp, 73.50.Td γ-ray radiation effect has been studied on transport and noise properties of high electron mobility transistors (HEMTs) with gate lengths in the range from 350 to 150 nm at room temperature. Current-voltage (I -V) characteristics of the devices demonstrate higher radiation hardness to 60 Co γ-rays up to doses of 10 9 Rad at larger gate lengths. This confirms the very important role of surface passivation for channel transport of the HEMTs. The deviation of the I -V characteristics parameters saturated current, transconductance, channel conductance, and threshold voltage does not exceed 20% at highest radiation dose. The noise spectra of pre-irradiated devices and after γ-irradiation show different frequency dependences corresponding to different fluctuation processes in the HEMTs. The results are confirmed by dynamic current measurements of the channel conductivity.
We address experimental and theoretical study of a two-dimensional electron gas transport at low and moderate electric fields. The devices under study are group-III nitride-based ͑AlGaN/GaN͒ gateless heterostructures grown on sapphire. The transmission line model patterns of different channel lengths, L, and of the same channel width are used. A strong dependence of the device I-V characteristics on the channel length has been found. We have developed a simple theoretical model to adequately describe the observed peculiarities in the I-V characteristics measured in steady-state and pulsed (10 Ϫ6 s) regimes. The effect of the Joule heating of a heterostructure is clearly distinguished. The thermal impedance and the channel temperature rise caused by the Joule self-heating have been extracted for the devices of different L at different values of dissipated power. The current reduction due to both self-heating and hot-electron effects is determined quantitatively as a function of the electric field.
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