Search

This paper describes an extensive analysis of the role of off-state and semi-on state bias in inducing the trapping in GaN-based power High Electron Mobility Transistors. The study is based on combined pulsed characterization and on-resistance transient measurements. We demonstrate that--by changing the quiescent bias point from the off-state to the semi-on state--it is possible to separately analyze two relevant trapping mechanisms: (i) the trapping of electrons in the gate-drain access region, activated by the exposure to high drain bias in the off-state; (ii) the trapping of hot-electrons within the AlGaN barrier or the gate insulator, which occurs when the devices are operated in the semi-on state. The dependence of these two mechanisms on the bias conditions and on temperature, and the properties (activation energy and cross section) of the related traps are described in the text. [ABSTRACT FROM AUTHOR]

In this paper, we report on the challenges related to growth and processing of 200 mm GaN-on-Si wafers in a CMOS fab. We describe the Au free process we developed as well as how we assure wafer quality prior processing. For the first time, we analyze possible Ga contamination issues related to the processing of GaN wafers and we present the cleaning procedures we developed to avoid it. [ABSTRACT FROM AUTHOR]

Abstract: In this work we report on the two most common failure modes for AlGaN/GaN-based HEMTs: the gate leakage increase and the output current drop. First, by performing step-stress experiments in function of the step-time (t STEP) we show that the critical voltage for the increase of gate leakage current depends on the t STEP and is not associated with a permanent drop of the output current. Consequently, identification of the critical voltage by means of step-stress is not meaningful per se since it depends on the t STEP used. Second, we show that during high power stress at high voltage a permanent output current drop occurs. The failure analysis reveals the formation of crystallographic defects in the AlGaN layer along the whole width of the gate, in agreement with the inverse piezoelectric theory. However, in contrast to the degradation model based on the inverse piezoelectric effect, these defects do not aid the leakage of electrons from the gate toward the drain electrode since the output current drop is not associated with an increase of the gate leakage current. Therefore, combining the outcome of the two experiments, we suggest that the two most common failure modes are not correlated despite both might concur to the device degradation. Finally, an excellent stability is shown for devices with reduced Al content in the AlGaN barrier, highlighting the fundamental role of strain on reliability of AlGaN/GaN-based devices. [Copyright &y& Elsevier]

Abstract: In this work, the impact of 1000h thermal storage test at 325°C on the performance of gallium nitride high electron mobility transistors grown on Si substrates (GaN-on-Si HEMTs) is investigated. The extensive DC- and pulse-characterization performed before, during and after the stress did not reveal degradation on the channel conduction properties as well as formation of additional trapping states. The failure investigation has shown that only the gate and drain leakage currents were strongly affected by the high temperature storage test. The physical failure analysis revealed a Au inter-diffusion phenomenon with Ni at the gate level, resulting in a worsening of the gate–AlGaN interface. It is speculated that this phenomenon is at the origin of the gate and drain leakage current increasing. [Copyright &y& Elsevier]

A novel normally-off AIN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMT) on 100-mm Si substrates for high-power applications is demonstrated for the first time by means of a selective thermal oxidation of AIN. The formation of a high-quality insulating AION layer resulting from the dry thermal oxidation of AIN at 900 ° C in oxygen has been identified by transmission electron microscopy and X-ray photoelectron spectroscopy. The AIN thermal oxidation appears to be highly selective toward the SiN cap layer allowing the local depletion of the 2-D electron gas (self-aligned to the gate) and thus the achievement of normally-off operation. Threshold voltage (VT) of +0.8 V and drain leakage current at VGS = 0 V well below 1 µA/mm are obtained reproducibly over the wafer. The comparison of the fabricated MOSHEMTs with the control sample (identical but nonoxidized) reveals a drastic shift of VT toward positive values and three to four orders of magnitude drain leakage current reduction. [ABSTRACT FROM AUTHOR]

This paper presents an extensive analysis of the off-state conduction mechanisms in AlGaN/GaN Meta–Insulator–Semiconductor (MIS) transistors. Based on combined bi-dimensional numerical simulation and experimental measurements, we demonstrate the following relevant results: (i) under off-state bias conditions, the drain current can show a significant increase when the drain bias is swept up to 600 V; (ii) several mechanisms can be responsible for off-state current conduction, including band-to-band tunneling and impact ionization; (iii) two-dimensional numerical simulations indicate that band-to-band tunneling plays a major role, while impact ionization does not significantly contribute to the overall leakage. Temperature-dependent I – V measurements were also carried out to identify the origin of the vertical drain-bulk leakage. [ABSTRACT FROM AUTHOR]

Abstract: Properties of stress-induced percolation paths in AlGaN in step-stressed AlGaN/GaN high electron mobility transistors are investigated in details. DC and transient gate and drain current analysis are combined with low frequency noise and electroluminescence measurements. The observation of random telegraph signal (RTS) noise with large relative amplitude indicates that RTS is due to modulation of gate current in the percolation path by action of single defects. Measurements of RTS amplitude as a function of forward or reverse gate voltage can reveal masked gate leakage current components related to individual percolation paths. The observed gradual increase in forward gate current ideality factor with progressing stress, indicating defect penetration inside the percolation path in AlGaN, is explained by a simple model. The role of slow trapping in the modulation of current in the percolation path is discussed too. [Copyright &y& Elsevier]