Metal-insulator-semiconductor High-electron-mobility Transistors Research Articles

Impact of process-dependent SiNx passivation on proton-induced degradation in GaN MIS-HEMTs

In this study, AlGaN/GaN heterojunction-based metal–insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) were fabricated using silicon nitride (SiN) passivation layer. This layer was deposited under the different gas ratio conditions. The effects of proton irradiation on the current characteristics of the devices were investigated according to the deposition conditions of the SiN film. The drain current (ID) characteristics of two devices (with Si-rich or N-rich SiN passivation layers) were reduced by proton irradiation regardless of the deposition condition of SiN film because of the proton-induced displacement damage. In terms of the threshold voltage (Vth), off-state current (Ioff) and gate leakage current (IG), the device with Si-rich SiN exhibited less variation after proton irradiation compared with the N-rich SiN device. This is because the Si-rich SiN was less affected by the proton irradiation. Furthermore, the device with Si-rich SiN showed better dynamic performances before and after proton irradiation than the device with N-rich SiN. This was achieved suppressing the drain-lag phenomenon because the high SiH4 rate for Si-rich SiN deposition considerably reduces the bulk trap states. The capacitance characteristics of the Si-rich SiN device were also improved by the high SiH4 rate. Therefore, the Si-rich SiN-passivated MIS-HEMTs achieved enhanced performance and higher reliability for applications involving space radiation.

Fabrication and analysis of InAlN/GaN metal–insulator–semiconductor high-electron-mobility transistors based on AlN/GaN superlattice channel

In this work, InAlN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) based on the AlN/GaN superlattice channel have been demonstrated. The devices fabricated with the AlN/GaN superlattice channel perform superior characteristics over other relative devices consisted of the conventional single GaN channel. The effective channel-electron mobility, maximum drain current, ON-resistance, and the ION/IOFF ratio of the superlattice-channel-based MIS-HEMTs are approximately 932 cm2 V−1 s−1, 57 mA/mm, 62 Ω mm, and 108 and those of the conventional structure are 820 cm2 V−1 s−1, 48 mA/mm, 92 Ω mm, and 104, respectively. Additionally, this work has shown that the AlN/GaN superlattice channel has the ability to suppress leakage currents. As a result, the breakdown voltage of the device based on the superlattice structure without the back barrier is approximately 500 V, which is 430 V higher than that based on the single GaN channel.

Temperature-dependent characteristics for the p-type CuO gate HEMT and high-k HfO2 MIS-HEMT on the Si substrates

This work presents the temperature-dependent characteristics of the thin-barrier Al0.45Ga0.55N/GaN high electron mobility transistor (HEMT), p-type CuO gate HEMT, and high-k HfO2 metal–insulator–semiconductor HEMT (MIS-HEMT). As the temperature rises from 20 to 300 °C, the maximum trans-conductance of the HfO2 MIS-HEMT and CuO gate HEMT reduces by 56.9% and 43.2%, respectively. The sub-threshold swing of the CuO gate HEMT is smaller than that of the HfO2 device when the temperature reaches 300 °C. According to the C–V test results from 20 to 300 °C, the relative dielectric constant of CuO increases from 18.1 to 47.4, whereas HfO2 has a relatively stable dielectric constant. The calculation models are presented to investigate the effect of the dielectric constant on the drain current and the trans-conductance. The calculated results show that the maximum transconductance of the HfO2 MIS-HEMT and CuO gate HEMT decreases by 52.3% and 38.9%, respectively, which is in good agreement with the experimental results.

Effects of Proton Irradiation on the Current Characteristics of SiN-Passivated AlGaN/GaN MIS-HEMTs Using a TMAH-Based Surface Pre-Treatment.

This study investigated the combined effects of proton irradiation and surface pre-treatment on the current characteristics of Gallium Nitride (GaN)-based metal-insulator-semiconductor high-electron-mobility-transistors (MIS-HEMTs) to evaluate the radiation hardness involved with the Silicon Nitride (SiN) passivation/GaN cap interface. The impact of proton irradiation on the static and dynamic current characteristics of devices with and without pre-treatment were analyzed with 5 MeV proton irradiation. In terms of transfer characteristics before and after the proton irradiation, the drain current of the devices without and with pre-treatment were reduced by an increase in sheet and contact resistances after the proton irradiation. In contrast with the static current characteristics, the gate-lag characteristics of the device with pre-treatment were significantly degenerated. In the device with pre-treatment, the hydrogen passivation for surface states of the GaN cap was formed by the pre-treatment and SiN deposition processes. Since the hydrogen passivation was removed by the proton irradiation, the newly created vacancies resulted in the degeneration of gate-lag characteristics. After nine months in an ambient atmosphere, the gate-lag characteristics of the device with pre-treatment were recovered because of the hydrogen recombination. These results demonstrated that the radiation hardness of MIS-HEMTs was affected by the SiN/GaN interface quality.

A novel GaN MIS‐HEMT with a floating clamp electrode for suppressing short‐channel effect

In this work, a novel GaN MIS-HEMT (metal-insulator-semiconductor high electron mobility transistors) featuring a floating clamp (FC) electrode is proposed for suppressing the short-channel effect. By inserting the FC electrode near to the drain-side gate edge, the transverse potential at the gate edge can be clamped to less than 2 V, thereby the short-channel effect can be suppressed. Compared to the conventional short-channel GaN MIS-HEMT, the proposed device exhibits much decreased off-state electron density at the drain voltage of 10 V, which leads to the off-state leakage current decreasing from 10–1 to 10–7 A/mm, without an obvious sacrifice of the on-state current. Meanwhile, the proposed GaN MIS-HEMT also delivers a much lower reverse gate-to-drain capacitor. The excellent characteristics of the proposed GaN MIS-HEMT show that the device is promising for the future power applications.

Well-suppressed interface states and improved transport properties of AlGaN/GaN MIS-HEMTs with PEALD SiN gate dielectric

SiN deposited by plasma-enhanced atomic layer deposition (PEALD) is investigated as gate dielectric layer for GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs). The X-ray photoelectron spectroscopy (XPS) confirms low oxygen content in SiN-layer and the interface of SiN/(Al)GaN. The fabricated MIS-HEMTs exhibit significant reduction in gate leakage current (two or three orders of magnitude) and improvement in drain current (ID) characteristics, compared with the controlled HEMTs. A remarkable small threshold voltage (VTH) hysteresis (0.12 ± 0.05 V) and an enhanced 2DEG channel mobility are also achieved for PEALD SiN/(Al)GaN MIS-HEMTs. Simultaneously, a distribution of the interface states is quantitatively described by constant-capacitance deep-level transient spectroscopy (CC-DLTS), displaying a low density of 1.6 × 1013 cm−2 eV−1 at level depth of 0.03 eV and below 2.1 × 1012 cm−2 eV−1 at deep level depth of EC - ET > 0.4 eV. The suppressed interface traps density results in an improved performance for MIS-HEMTs. The dependence of the characteristics of MIS-HEMTs on SiN thickness (tSiN) was also studied in detail.

Demonstration of vertically-ordered h-BN/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors on Si substrate

AlGaN/GaN metal–insulator-semiconductor high-electron-mobility transistors (MISHEMTs) have been demonstrated with 22 nm thick vertically ordered (VO) h-BN by high-power impulse magnetron sputtering deposited at room temperature for the first time. About two orders of magnitude lower gate leakage current was observed in VO h-BN/AlGaN/GaN MIS-diodes compared to conventional Schottky diodes. The fabricated MISHEMT and HEMT with 2 µm gate-length exhibited a maximum drain current density (IDmax) of 685 and 467 mA/mm and a maximum extrinsic transconductance (gmmax) of 93 and 134 mS/mm, respectively. The VO h-BN/AlGaN/GaN MISHEMT with improved characteristics is due to an enhanced sheet carrier density (from 7.29 × 1012 cm−2 to 1.10 × 1013 cm−2) by surface passivation of VO h-BN as well as the good VO h-BN/GaN interface quality with a minimum interface state density of 2.6 × 1012 cm-2eV−1.

Monolithic Comparator and Sawtooth Generator of AlGaN/GaN MIS-HEMTs With Threshold Voltage Modulation for High-Temperature Applications

This article demonstrates the integrated comparators, hysteresis comparators, and sawtooth generators based on aluminum-gallium-nitride/gallium-nitride (AlGaN/GaN) metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). The integrated circuits (ICs) exhibit thermal stability from 25 °C to 250 °C in both static and transient performances. The threshold voltage ( V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) in depletion (D)-mode MIS-HEMT is modulated from -8.9 to -2.4 V to optimize the performance of integrated comparator circuits. The comparator can realize a large and stable comparison range of 3-9 V and a high voltage swing of 9.1 V, while the hysteresis comparator exhibits a good noise-immunity ability and stable hysteresis output. The sawtooth generator with the hysteresis comparator features a high amplitude (6.1 V) sawtooth signal at 500 kHz to realize a compact structure applicable to the high-voltage mixed-signal circuits. These results show the feasibility of MIS-HEMT monolithic comparator circuits in conversion systems.

Obtaining impact ionization-induced hole current by electrical measurements in gallium nitride metal–insulator–semiconductor high electron mobility transistors

In this paper, an extraction method for measuring impact ionization-induced hole current in gallium nitride (GaN) metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) is proposed. The results show that the non-monotonic impact ionization current characteristic can be easily acquired by the extraction method. Further, different hot-carrier stress (HCS) conditions can be obtained based on the I G–V G curve, and the reliability tests can act as verification of the impact-ionization curve. In addition, electrical reliability tests indicate that the threshold voltage (V TH) shift and on-state current (I on) degradation in the MIS-HEMTs have a positive correlation to impact ionization-generated hole current. During HCS operation, the V TH will shift positively and I on decreases due to hot electrons trapping into the GaN layer. This model is validated by TCAD simulation.

A Low Program Voltage Enabled Flash like AlGaN/GaN Stack Layered MIS-HEMTs Using Trap Assisted Technique

In this paper, a flash like Al2O3/SiO2 stacked layer AlGaN/GaN-based metal insulator semiconductor high electron mobility transistor (MIS-HEMT) was fabricated using trap assisted technique. The MIS-HEMT showed a large positive shifting of threshold voltage (∆VTH) of 4.6 V after applying a low program voltage (VP) of 3 V, resulting in a very low threshold voltage of −0.3 V with a decent maximum drain current (IDMAX) of 575 mA mm−1. A ultraviolet-ozone (UV/O3) surface treatment was done prior to gate dielectric deposition to produce a thin gallium oxynitride (GaOXNY) layer at GaN/oxide interface, which correspondingly acts as a charge trapping layer, resulting in the reduction in VP. The capacitance-voltage (C–V) measurements revealed that the traps contributing to the significant positive shifting of VTH had a density of 5.7 × 1012 cm−2. These traps were attributed to the border or oxide defects. A significant reduction in gate leakage current (IG) of more than three orders of magnitude was found in MIS-HEMT, due to the high quality Al2O3/SiO2 stack gate dielectric layer compared to conventional HEMT. The flash like stack layered programmed MIS-HEMT exhibited a GMMAX of 123 mS mm−1, on-off ratio of 1.7 × 107, subthreshold slope of 121 mV dec−1 with a reduced gate leakage current of 7.5 × 10−9 A mm−1.

Analysis of High-Frequency Behavior of AlGaN/GaN HEMTs and MIS-HEMTs under UV Illumination

The high-frequency characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) and metal-insulator-semiconductor HEMTs (MIS-HEMTs) are investigated under ultraviolet (UV) radiation with 365 nm wavelength. When HEMTs and MIS-HEMTs are illuminated with an UV source, their drain currents increase apparently owing to the generated photocurrent. Nevertheless, they show different high-frequency response to the UV light. For HEMTs, the peak cutoff frequency (fT) and maximum oscillation frequency (fmax) of illuminated devices are 20% and 10% higher than those in dark condition, respectively, owing to the increased transconductance. For MIS-HEMTs, however, their high-frequency performances are degraded when transistors are subject to light exposure. The degradations of peak fT and fmax are around 3.7% and 18%, respectively. The small-signal model parameters relevant to the high-frequency characteristics were extracted to explain these phenomena. Additional trapped charges in the SiN gate dielectric induced by UV light would be responsible for the degraded high-frequency parameters in illuminated MIS-HEMTs. These experimental results are important for designing a suitable GaN-based HEMT for optoelectronic applications.

Substrate Bias Enhanced Trap Effects on Time-Dependent Dielectric Breakdown of GaN MIS-HEMTs

In this work, we present the substrate bias enhanced trap effects on time-dependent dielectric breakdown (TDDB) in GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) by experiment. Under different substrate biases, the shape parameter β and scale factor η of the Weibull distribution are extracted from the experimental data. A monotonical decrease in β from intrinsic breakdown to extrinsic breakdown relating to the hole-emission from the acceptor-like buffer traps with increased negative substrate biases has been observed, while η is increased at large positive substrate biases. This unexpected increase in η suggests that the donor-like buffer traps play an important role with a longer lifetime. The trap mechanisms, relating to percolation path establishment, are analyzed based on progressive breakdown (PBD). The capacitance-voltage characteristics are measured during each stress cycle confirming the hole fluence and electron injection in the gate-stack layer with different trap distributions under various substrate biases. Finally, 2-D device simulations are carried out to probe for physical insight into the traps on TDDB failure mechanisms.

A Study of the Gate-Stack Small-Signal Model and Determination of Interface Traps in GaN-Based MIS-HEMTs

The existing gate-stack small-signal models of metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) were analyzed, and a new model that could fit the measured admittance characteristics in the whole bias regime after learning about their shortcomings was presented. The capacitance and conductance frequency characteristics were fitted simultaneously, and the extracted fitting parameters showed reasonable values and trends. These parameters were then used in the determination of interface traps as well as the quantitative analysis of two C-V slopes for MIS-HEMTs. It was proven that the intrinsic barrier resistance was also a critical factor for the second slope. Thus, this resistance could not be neglected by the capacitance method that determined the interface trap densities directly by the frequency dispersion of the second slope. This article extracted the energy distribution of the interface trap density, which could be fitted by a Gaussian distribution with a maximum value of ~ 3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . Although this method was a suitable alternative because the capacitance and conductance were correlated by the admittance characteristics, the detected shallow-level traps may not account for the threshold voltage drift or other reliability problems of MIS-HEMTs.

Monolithic Integrated Normally OFF GaN Power Device With Antiparallel Lateral Schottky Barrier Controlled Schottky Rectifier

Integration of an enhancement-mode (E-mode) metal–insulator–semiconductor high-electron-mobility transistor (MIS-HEMT) with a high-performance lateral Schottky barrier controlled Schottky (LSBS) rectifier in a compact layout is fabricated on an ultrathin-barrier AlGaN/GaN heterostructure grown on Si substrate. The state-of-the-art reverse conduction voltage ( ${V}_{{\text {rev}}}$ ) of 0.455 V was achieved in the monolithic integrated E-mode power device with a threshold voltage of 1.55 V. ${V}_{{\text {rev}}}$ exhibited a tiny temperature variation of 0.66% from 0 °C to 150 °C compared with that of 157% for the controlled E-mode HEMT.

Mechanisms Underlying the Bidirectional V T Shift After Negative-Bias Temperature Instability Stress in Carbon-Doped Fully Recessed AlGaN/GaN MIS-HEMTs

In this brief, we investigate the bidirectional threshold voltage drift ( $\Delta {V}_{T}$ ) following negative-bias temperature instability (NBTI) stress in carbon-doped fully recessed AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs). Several stress conditions were applied at different: 1) gate biases ( ${V}_{GS,STR}$ ); 2) stress times ( ${t}_{STR}$ ); and 3) temperatures ( ${T}$ ). Both negative and positive $\Delta {V}_{T}$ (thermally activated with different activation energies, ${E}_{A}$ ) were observed depending on the magnitude of ${V}_{GS,STR}$ . In accordance with the literature, observed $\Delta {V}_{T} V ( ${E}_{A}~\approx ~0.5$ eV) under moderate stress is attributed to the emission of electrons from oxide and interface traps. Instead, $\Delta {V}_{T} >0$ V ( ${E}_{A}~\approx ~0.9$ eV) under high stress is attributed to the increased negatively ionized acceptor trap density in the buffer associated with carbon doping.

Suppression of interface states between nitride-based gate dielectrics and ultrathin-barrier AlGaN/GaN heterostructure with in situ remote plasma pretreatments

A silicon nitride (SiNx) film deposited at 500 °C by plasma-enhanced atomic layer deposition (PEALD) is employed as the gate dielectric for GaN-based metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs). An interface enhancement technology featuring in situ low-damage NH3/N2 remote plasma pretreatments (RPPs) is developed prior to the SiNx gate dielectric deposition, which contributes to an improved surface morphology while remarkably suppressed interface oxides. It is revealed by constant-capacitance deep-level transient spectroscopy that both shallow and deep states at the PEALD-SiNx/III-nitride interface are reduced by about one order of magnitude by the RPP. The in situ RPP and PEALD-SiNx gate dielectric process are implemented into fabrication of enhancement-mode MIS-HEMTs on an ultrathin-barrier AlGaN/GaN heterostructure technology platform. The fabricated MIS-HEMTs deliver an improved threshold stability and maximum output current as compared with devices without the RPP.

AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs) using plasma deposited BN as gate dielectric

AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs) were fabricated on Si substrates with a 10 nm boron nitride (BN) layer as a gate dielectric deposited by electron cyclotron resonance microwave plasma chemical vapor deposition. The material characterization of the BN/GaN interface was investigated by X-ray photoelectric spectroscopy (XPS) and UV photoelectron spectroscopy. The BN bandgap from the B1s XPS energy loss is ∼5 eV consistent with sp2 bonding. The MISHEMTs exhibit a low off-state current of 1 × 10−8 mA/mm, a high on/off current ratio of 109, a threshold voltage of −2.76 V, a maximum transconductance of 32 mS/mm at a gate voltage of −2.1 V and a drain voltage of 1 V, a subthreshold swing of 69.1 mV/dec, and an on-resistance of 12.75 Ω·mm. The interface state density (Dit) is estimated to be less than 8.49 × 1011 cm−2 eV−1. Gate leakage current mechanisms were investigated by temperature-dependent current–voltage measurements from 300 K to 500 K. The maximum breakdown electric field is no less than 8.4 MV/cm. Poole–Frenkel emission and Fowler–Nordheim tunneling are indicated as the dominant mechanisms of the gate leakage through the BN gate dielectric at low and high electric fields, respectively.

GaN MIS-HEMTs With Surface Reinforcement for Suppressed Hot-Electron-Induced Degradation

We report a processing technique to form a surface reinforcement layer (SRL) in GaN metal-insulator-semiconductor high-electron mobility transistors (MIS-HEMTs) with the aim to suppress device dynamic on-resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> ) degradation caused by long-term hot-electron stress. The SRL is a crystalline (Al)GaON layer formed by reconstruction of the heterojunction surface through plasma oxidation and high temperature annealing. MIS-HEMTs with SRL exhibit substantially suppressed dynamic R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> degradation than the conventional devices without SRL, after long-term hot-electron stress. The (Al)GaON SRL exhibits substantially enhanced thermal stability and strong immunity to energetic carriers. The SRL-enabled suppression of hot-electron-induced degradation is further verified by the electroluminescence characterizations.

Pt-Decorated Graphene Gate AlGaN/GaN MIS-HEMT for Ultrahigh Sensitive Hydrogen Gas Detection

Hydrogen fuel has attracted significant attention as an alternative clean energy for hydrogen vehicles and household fuel systems and has been expected to be pervasive. Thus, compact, low-power, and highly sensitive hydrogen sensors capable of being embedded in Internet-of-Things devices are in demand. In this work, an ultrahigh sensitive hydrogen sensor operating at room temperature based on the Pt-decorated graphene (Pt/Gr) gate AlGaN/GaN metal–insulator–semiconductor high electron mobility transistor (MIS-HEMT) is presented. The proposed unique gate structure of island-like Pt on graphene not only modulates the density of 2-D electron gas (2DEG) but also provides efficient diffusion of hydrogen ions into the gate even at very low concentrations ( $\sim 1.6\times 10^{7}$ in a hydrogen concentration of 1000 ppm at room temperature. Upon exposure of at most 1 ppm hydrogen gas, the current increases significantly by a factor of 15.4, exhibiting an unprecedentedly high hydrogen response. Furthermore, the proposed AlGaN HEMT architecture has an outstanding hydrogen selectivity and insensitivity to NH3, H2S, and CO gases at the same time.

Numerical Study of Novel GaN HEMTs With Integrated SBDs for Ultrahigh Reverse Conduction Capability

This brief proposes novel integrated GaN high-electron-mobility transistor (HEMT) with multichannel Schottky barrier diode (SBD) structures to achieve ultrahigh reverse conduction capability and maintain the blocking characteristic at the same time. The simulative results indicate that the reverse voltage drop and reverse ON-state resistance can be reduced by 38.6% and 38% compared with the traditional metal–insulator–semiconductor HEMT, respectively. Meanwhile, the forward conduction capability, the blocking performances, and the capacitance characteristics are little influenced. Moreover, it is proved that the proposed devices also exhibit superior dynamic performances, indicating the application potential of reducing the power loss of power electronic systems. Finally, the key fabrication flows for the novel devices are presented and discussed.