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In this work, the breakdown characteristics and the electroluminescence (EL) spectra of a Schottky-metal/p-GaN/AlGaN/GaN device under forward bias were investigated at different temperatures. The failure of the metal/p-GaN junction, which was caused by electron transport in the p-type Schottky junction, was identified as the first step in the device breakdown process. The breakdown voltage increased with higher temperatures. Under a forward bias of 8 V, the intensity of the EL emission increased more than two orders of magnitude, while the current increased by a factor of 4 as the temperature increased from 0 °C to 200 °C. This unambiguously demonstrated thermally enhanced hole injection at the Schottky-metal/p-GaN interface. We proposed that more electrons were annihilated by the thermally enhanced hole injection, resulting in the positive temperature dependence of the device breakdown. [ABSTRACT FROM AUTHOR]

In this letter, we investigated the electroluminescence (EL) spectra and photovoltage spectrum of a Schottky-metal/ ${p}$ -GaN/AlGaN/GaN diode with a semitransparent anode electrode. By analyzing the bias-dependence of the EL spectra of the diode as well as the gate stress bias-/time- dependences of the threshold voltage shift of a ${p}$ -GaN gate HEMT, the electron/hole injection sequence, electron trapping, hole-assisted de-trapping, and optical pumping processes in the ${p}$ -GaN gate region are identified. The band diagrams of the Schottky-metal/ ${p}$ -GaN/AlGaN/GaN heterostructure under different forward bias voltages are proposed. [ABSTRACT FROM AUTHOR]

The gate structure of a ${p}$ -(Al)GaN gate AlGaN/GaN high electron mobility transistor (HEMT) is a direct bandgap hetero-PN junction, which emits light under forward bias above the threshold voltage. This internal light emission induces persistent photoconductivity (PPC) of the GaN channel/buffer layer, leading to the increase in OFF-state leakage current. In this letter, we studied the OFF-state leakage degradation induced by ON-state gate drive of a ${p}$ -GaN gate HEMT. Two self-limiting functions are discovered: 1) saturation of the increment of leakage current under continuous pulse operations and 2) dramatically enhanced recovery speed of the internal light-emission-induced PPC effect at elevated temperatures. This letter indicates the robustness of ${p}$ -(Al)GaN gate HEMTs in switching applications in spite of the seemingly inevitable leakage current degradation. [ABSTRACT FROM AUTHOR]

In this letter, we investigate the threshold voltage ( ${V}_{\text {TH}}$ ) shift in a p-GaN gate AlGaN/GaN transistor by designed gate-bias pulse measurements. It was found that the forward gate bias causes positive ${V}_{\text {TH}}$ shift. The dynamics of electron trapping was revealed from the dependences of the consequent ${V}_{\text {TH}}$ shift on the bias duration at different voltages. A time constant smaller than 0.1 ms for the ${V}_{\text {TH}}$ shift saturation at 6-V gate bias was obtained. It was also found that the ${V}_{\text {TH}}$ became inversely proportional to the gate-bias voltages exceeding 7 V. This inverse proportionality of the ${V}_{\text {TH}}$ shift resulted from the threshold of the hole-injection/electroluminescence (EL) and the sequential optical pumping effect on the electron traps. The EL emission was confirmed by a self- and in-situ photon detection measurement. [ABSTRACT FROM AUTHOR]

A systematic analytical investigation of the charge distribution and gate control of the normally-off GaN double-channel MOS-HEMT (DC-MOS-HEMT) is presented in this paper. Compared to conventional GaN MOS-HEMT, the DC-MOS-HEMT features a thin AlN insertion layer (AlN-ISL) below the original two dimensional electron gas (2DEG) channel, thus forming a second channel at the interface between AlN-ISL and the underlying GaN. This paper reveals the impact of the AlN-ISL on the 2DEG distribution and the gate control of the channels. The sensitivity of ${V}_{\text {th}}$ against the recess depth is also analytically studied and is found to be nearly independent of the recess depth as long as the recess is terminated in the upper channel layer. The analytical results are well supported by numerical device simulations, and the physical mechanisms behind these findings are explained along with the analytical investigations. [ABSTRACT FROM AUTHOR]

A previously reported normally-off GaN double-channel (DC-) MOS-HEMT with a gate recess into the upper channel layer has achieved a remarkably low R\text {on} . In this letter, we found that the double-channel structure itself does not guarantee a low R\text {on} without careful consideration of the electrical coupling between the two channels. A strong channel-to-channel (C2C) coupling between the two channels is critical to reduce R\text {on} in the DC-MOS-HEMT by exploiting both channels at the access region while allowing currents to converge into the heterojunction lower channel at the gate region. Otherwise, with a weak C2C coupling, the conduction through the upper channel is comprised due to the high-resistivity MOS-channel section at the gate region. The fabricated DC-MOS-HEMT with C2C distance ( t{\textsf {C2C}} ) of 7.5 nm exhibits an appreciably lower R\text {on} than that with t{\textsf {C2C}} = \textsf {11.5} nm. Further analysis reveals the latter suffers from an increased sheet resistance at access region compared with the sheet resistance of the DC-heterostructure itself. A modified TLM characterization is proposed to analyze the C2C coupling in the DC-heterostructure. It is confirmed the DC-heterostructure with t{\textsf {C2C}} = \textsf {7.5} nm boasts a strong C2C coupling, while that with t{\textsf {C2C}} = \textsf {11.5} nm features relatively weak C2C coupling. [ABSTRACT FROM PUBLISHER]

In this paper, we report a systematic study of the nitridation effects on GaN surface by first-principles calculations and X-ray/ultraviolet photoemission spectroscopy (XPS/UPS). According to the calculated electronic structures, two surface bands (i.e., the upper band and the lower band) can be seen within the bandgap for the typical surface configurations that may occur in the experimental condition as a result of surface reconstruction. By the deployment of sufficient nitridation, the energy positions of the lower band are modified toward the valence band by ~1 eV, resulting in the overlapping of the lower surface band with the valence band. Meanwhile, the upper surface band is also modified toward the valence band, but by a smaller amount. The modification to the positions of the surface bands is furthermore manifested by XPS/UPS spectra characterization performed on GaN sample that underwent surface treatment with low-energy remote N2 plasma. The theoretical and experimental results insightfully proclaim the nitridation effects on material properties at atomic level, and support a surface-state ionization model for the GaN band-edge (3.4 eV) emission in metal-AlGaN/GaN Schottky-on-heterojunction diode under forward bias. [ABSTRACT FROM PUBLISHER]

Integration of a photon source into the AlGaN/GaN high election mobility transistor (HEMT) platform will realize the functionality of on-chip optical pumping of deep electron traps which suppress the dynamic performances of power HEMTs. Here, we report a Schottky-on-heterojunction light-emitting diode (SoH-LED) realized on the p-doping-free lateral AlGaN/GaN heterostructure. A physical mode based on hot electron induced surface states impact ionization was proposed to explain the hole generation and injection processes in this p-doping-free SoH-LED. Since the SoH-LED shares identical epitaxial structures with HEMT, integration of SoH-LED and HEMT requires no additional epi-layers during the wafer growth and minimum process modification during device fabrication. The SoH-LED structure was seamlessly integrated into the HEMT platform as an on-chip photon source. Experiment results showed that the SoH-LED photons can effectively assist the electron de-trapping processes from both of the surface and bulk deep traps, demonstrating the feasibility of using on-chip generated photons to improve the dynamic performances of AlGaN/GaN power HEMTs. [ABSTRACT FROM AUTHOR]

A low on-resistance normally-off GaN double-channel metal–oxide–semiconductor high-electron-mobility transistor (DC-MOS-HEMT) is proposed and demonstrated in this letter, which features a 1.5-nm AlN insertion layer (ISL) located 6 nm below the conventional barrier/GaN interface, forming a second channel at the interface between the AlN-ISL and the underlying GaN. With gate recess terminated at the upper channel, normally-off operation was obtained with V\mathrm {th} of +0.5 V at I\mathrm {DS}= 10 ~\mu \text{A} /mm or +1.4 V from the linear extrapolation of the transfer curve. The lower heterojunction channel is separated from the etched surface in the gate region, thereby maintaining its high field-effect mobility with a peak value of 1801 cm2/( \textV\cdot \texts ). The on-resistance is as small as 6.9 \Omega \cdot \text mm for a DC-MOS-HEMT with LG/L\mathrm {GS}/L\mathrm {GD} = 1.5/2/15~\mu \text{m} , and the maximum drain current is 836 mA/mm. A high breakdown voltage (>700 V) and a steep subthreshold swing of 72 mV/decade are also obtained. [ABSTRACT FROM AUTHOR]

Effective interface engineering techniques in III-nitride heterojunction power devices, aiming at yielding high VTH stability in insulated-gate devices and suppressed current collapse in high-voltage switching operation, are of critical significance to enhance device performance and reliability. In this work, we present an interface enhancement technology featuring in situ low-damage NH3/Ar/N2 pre-gate plasma treatment prior to the ALD-Al2O3 deposition for high-performance III-nitride MIS-HEMTs. It is manifest that this technology can effectively remove the native oxide while forming a monocrystal-like nitridation interfacial-layer (NIL) on the III-nitride surface. The Al2O3(NIL)/GaN/AlGaN/GaN MIS-heterostructures with high-quality interface exhibit well-behaved electrical characteristics, including a small subthreshold swing of ∼64 mV/dec, a small hysteresis of ∼0.09 V, tiny f/T dispersions in the C- V characteristics, and low interface trap density of ∼1 × 1012-6 × 1012 cm−2eV−1. Cross-sectional TEM micrograph of the Al2O3/III-nitride gate stack with a monocrystal-like nitridation interfacial-layer (NIL). [ABSTRACT FROM AUTHOR]

Al2O3–AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) featuring indium tin oxide transparent gate electrode are fabricated for the purpose of evaluating the gate reliability. The transparent gate electrode allows electroluminescence (EL) observation in the region directly under the gate, which cannot be performed in conventional MIS-HEMTs with opaque gate electrode. Normally OFF transparent-gate MIS-HEMTs were realized by implanting fluorine ions into the AlGaN barrier prior to the deposition of Al2O3. The dependence of EL on bias condition was investigated with the color of EL resolved by filters. Gate dielectric degradation in MIS-HEMTs was induced by OFF state drain-bias stress, as detected by the increased gate leakage current. Location of the gate degradation could be clearly identified by EL imaging through the transparent gate. From the EL image, the passivation layer under the overhang of T-shaped gate is found to be vulnerable to OFF-state stress, which is confirmed by simulation. [ABSTRACT FROM AUTHOR]

The degradation of transient OFF-state leakage current in AlGaN/GaN HEMTs induced by ON-state gate overdrive was observed and studied. The OFF-state leakage current increases significantly with a pre- ON-state gate overdrive. It takes more than 30 s for the leakage current decay to its equilibrium level in dark. The decay processes follow a stretched-exponential law. We propose that this degradation corresponds to the persistent photoconductivity of GaN buffer induced by the electroluminescence during the Schottky gate overdrive. Both the ON-state gate overdrive bias and duration dependences of the OFF-states leakage degradation were studied. This work indicates that gate-protection is necessary to preserve low OFF-state leakage current and improve device reliability. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The GaN-to-Si vertical conduction mechanisms on a low resistivity p-type (111) Si substrate under high-voltage operation are investigated using the temperature-dependent high-voltage C-V characterization and device simulation. It is found the deep depletion and weak inversion in Si will result in a high electric field at the GaN/Si interface and induce the impact ionization of Si. The generated electrons will be injected into GaN buffer layer, fill in buffer traps and act as free carriers in GaN, eventually leading to considerable vertical leakage in the AlGaN/GaN-on-Si structures. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]