Evidence of relationship between strain and In-incorporation:Growth of N-polar In-rich InAlN buffer layer by OMCVD

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Insulated gate and surface passivation structures for GaN-based power transistors

Recent years have witnessed GaN-based devices delivering their promise of unprecedented power and frequency levels and demonstrating their capability as an able replacement for Si-based devices. High-electron-mobility transistors (HEMTs), a key representative architecture of GaN-based devices, are well-suited for high-power and high frequency device applications, owing to highly desirable III-nitride physical properties. However, these devices are still hounded by issues not previously encountered in their more established Si- and GaAs-based devices counterparts. Metal–insulator–semiconductor (MIS) structures are usually employed with varying degrees of success in sidestepping the major problematic issues such as excessive leakage current and current instability. While different insulator materials have been applied to GaN-based transistors, the properties of insulator/III-N interfaces are still not fully understood. This is mainly due to the difficulty of characterizing insulator/AlGaN interfaces in a MIS HEMT because of the two resulting interfaces: insulator/AlGaN and AlGaN/GaN, making the potential modulation rather complicated. Although there have been many reports of low interface-trap densities in HEMT MIS capacitors, several papers have incorrectly evaluated their capacitance–voltage (C–V) characteristics. A HEMT MIS structure typically shows a 2-step C–V behavior. However, several groups reported C–V curves without the characteristic step at the forward bias regime, which is likely to the high-density states at the insulator/AlGaN interface impeding the potential control of the AlGaN surface by the gate bias. In this review paper, first we describe critical issues and problems including leakage current, current collapse and threshold voltage instability in AlGaN/GaN HEMTs. Then we present interface properties, focusing on interface states, of GaN MIS systems using oxides, nitrides and high-κ dielectrics. Next, the properties of a variety of AlGaN/GaN MIS structures as well as different characterization methods, including our own photo-assisted C–V technique, essential for understanding and developing successful surface passivation and interface control schemes, are given in the subsequent section. Finally we highlight the important progress in GaN MIS interfaces that have recently pushed the frontier of nitride-based device technology

Annealing of Schottky contacts deposited on dry etched AlGaN/GaN,

The influence of annealing on properties of Pt Schottky contacts deposited on the electron cyclotron resonance plasma etched surface of an AlGaN/GaN heterostructure has been investigated. It is found that rapid thermal annealing (450 ◦C and 40 s in nitrogen gas), performed after metal deposition, allows for the preparation of Schottky contacts with similar or better properties than those obtained on a non-etched surface. This procedure is suitable for the realization of recessed high-quality Schottky contacts of AlGaN/GaN HEMTs

Determination of channel temperature in AlGaN/GaN HEMTs grown on sapphire and silicon substrates using DC characterization method

Self-heating effects and temperature rise in AlGaN/GaN HEMTs grown on silicon and sapphire substrates are studied, exploiting transistor dc characterization methods. A negative differential output resistance is observed for high dissipated power levels. An analytical formula for a source-drain current drop as a function of parasitic source resistance and threshold voltage changes is proposed to explain this behavior. The transistor source resistance and threshold voltage is determined experimentally at different elevated temperatures to construct channel temperature versus dissipated power transfer characteristic. It is found that the HEMT channel temperature increases rapidly with dissipated power and at 6 W/mm reaches values of 320 C for sapphire and 95 C for silicon substrate, respectively

Degradation Mechanisms in AlGaN/GaN HEMTs under Electrostatic Overstress

We study degradation mechanism in AlGaN/GaN HEMTs under 100 ns long rectangular current pulses applied on the drain contact. Devices were dc characterized after consecutive current stresses. We observed a sudden increase of source and drain resistances after the stress of 1.65 A. We used a backside transient interferometric mapping technique to localize the current path in the device during stresses. We revealed a current filamentation during stresses and dark spots formation in the position corresponding to filaments occurrence. We assume electron injection into the device buffer layer and an electromigration on contacts

Growth evolution of N-polar indium-rich InAlN layer on c-sapphire via strain relaxation by ultrathin AlON interlayer

International audienceInAlN as a functional inorganic material is a promising alternative to the commonly used InGaN in tunnel diodes and optoelectronic devices, due to its tunable wider range of energy bandgap (0.65-6.2 eV), thus empowering utilization of the whole solar spectrum. Moreover, high electron drift velocity and carrier concentration are considered as the most desirable prerequisite of indium-rich InAlN. N-polar indium-rich InAlN could be more beneficial due to the reverse direction of the polarization compared to Ga-polar. However, unanswered questions persist concerning growth evolution of N-polar indium-rich InAlN grown by organometallic chemical vapor deposition (OMCVD). In this study, energy dispersive X-ray spectroscopy (EDX) and high-angle annular dark-field (HAADF) imaging are used to characterize N-polar layer at nanometer scale in order to determine the evolution of the layer on (0001) sapphire substrate. Long nitridation of sapphire substrate leading to the formation of~2 nm AlON ultrathin interlayer, which relaxes strain at the InAlN/sapphire interface with assistance of a low-temperature AlN interlayer is observed. EDX analysis confirms that after strain relaxation of InAlN layer, the indium-incorporation has only a weak dependence on the polarity of the layer. The incorporation of indium at preferential sites is also discussed at length

Material and Device Issues of AlGaN/GaN HEMTs on Silicon Substrates

Selected material and device issues related to the performance of AlGaN/GaN HEMTs on (111) Si substrates are reported. It is shown that these devices can sustain significantly higher dc power (16 W/mm) than those grown on sapphire. Consequently smaller degradation in the device performance at higher temperatures (up to 400 8C) is demonstrated. Photoionisation spectroscopy reveals trap level of 1.85 eV, additional to two another levels found before in GaN-based HEMTs prepared on sapphire. Thus, AlGaN/GaN HEMTs on Si substrates demonstrate the viability of this technology for commercial application of high power rf devices