Effects of residual C impurities and Ga vacancies on the dynamic instabilities of AlN/AlGaN/GaN metal insulator semiconductor high electron mobility transistors are investigated. Secondary ion mass spectroscopy, positron annihilation spectroscopy, steady state and time-resolved photoluminescence (PL) measurements have been performed in conjunction with electrical characterization and current transient analyses. The correlation between yellow luminescence (YL), C- and Ga vacancy concentration is investigated. Time-resolved PL indicating the C$_{\mathrm{N}}$O$_{\mathrm{N}}$ complex as the main source of the YL, while Ga vacancies or related complexes with C seem not to play a major role. The device dynamic performance is found to be significantly dependent on the C concentration close to the channel of the transistor. Additionally, the magnitude of the YL is found to be in agreement with the threshold voltage shift and with the on-resistance degradation. Trap analysis of the GaN buffer shows an apparent activation energy of $\sim$0.8eV for all samples, pointing to a common dominating trapping process and that the growth parameters affect solely the density of trap centres. It is inferred that the trapping process is likely to be directly related to C based defects.
In this work, AlGaN/GaN HEMTs with dual-layer SiNx stressors (composed of a low-stress layer and a high-stress layer) were investigated. The low-stress padding layer solved the surface damage problem caused during the deposition of the high-stress SiNx, and provided a good passivated interface. The HEMTs with dual-layer stressors showed a 1 V increase in the threshold voltage (Vth) with comparable on-current and RF current gain to those without stressors. Moreover, the off-current (I_off) was shown to be reduced by one to three orders of magnitude in the strained devices as a result of the low…
Due to the piezoelectric nature of GaN, the 2DEG in AlGaN/GaN HEMT could be engineered by strain. In this work, SiNx deposited using dual-frequency PECVD was used as a stressor. The output performance of the devices was dominated by the surface passivation instead of the stress effect. However, the threshold voltage was increased by the induced stress, supporting strain engineering as an effective approach to pursue the normally-off operation of AlGaN/GaN HEMTs.
Mechanical transfer of high performing thin film devices onto arbitrary substrates represents an exciting opportunity to improve device performance, explore non-traditional manufacturing approaches, and paves the way for soft, conformal, and flexible electronics. Using a two-dimensional (2D) boron nitride (BN) release layer, we demonstrate the transfer of AlGaN/GaN high-electron mobility transistors (HEMTs) to arbitrary substrates through both direct van der Waals (vdW) bonding and with a polymer adhesive interlayer. No device degradation was observed due to the transfer process, and a signifi…
In this letter, we report on a unique device design strategy for increasing the breakdown voltage and hence Baliga Figure of Merit (BFOM) of III-nitride HEMTs by engineering the gate edge towards the drain. The breakdown of such devices with meandering gate-drain access region (M-HEMT) are found to be 62% more compared to that of conventional HEMT while the ON resistance suffers by 76%, leading to an overall improvement in the BFOM for by 28%. 3D-TCAD simulations show that the decrease in the peak electric field at the gate edge was responsible for increased breakdown voltage.
Characteristic electrical curves of GaN HEMT devices from Infineon and Transphorm are compared at different X-ray radiation dose. It is shown that the device with pGaN gate is more robust having a stable threshold voltage (Vth). The Vth of device with MIS gate shifts towards negative direction firstly and shifts to forward direction then. A qualitative analysis is performed in the paper. Such dynamic phenomenon is caused by releasing and trapping effects of radiation induced charges both in the dielectric layer and the interface of the device. It is summarized that pGaN gate based GaN HEMT is …
In this letter, we report the operation of AlGaN/GaN HEMTs with Pd gates in air over a wide temperature range from 22$^\circ$C to 500$^\circ$C. The variation in the threshold voltage ($V_{th}$) is less than 1$\%$ over the entire temperature range. Moreover, a safe biasing region where the transconductance peak ($g_m$) occurs over the entire temperature range was observed, enabling high-temperature analog circuit design. Furthermore, the operation of the devices over 25 hours was experimentally studied, demonstrating the stability of the DC characteristics and $V_{th}$ at 400$^\circ$C. Finally,…
The reliability of AlGaN/GaN HEMTs adopting Fe and C co-doping, with high and low carbon doping concentration was investigated by means of different stress tests. Firstly, DC and pulsed I-V characterization at room temperature are discussed, then drain step stress tests at different gate voltages are compared, afterwards, the constant stress at different bias points are discussed. Results show that the high C HEMTs showed reduced DIBL, smaller leakage current, as well as decreased electric field, leading to an improved robustness during on-state stress testing, with respect to the reference on…
We report on the interfacial electronic properties of HfO2 gate dielectrics both, with GaN towards normally-OFF recessed HEMT architectures and the AlGaN barrier for normally-ON AlGaN/GaN MISHEMTs for GaN device platforms on Si. A conduction band offset of 1.9 eV is extracted for HfO2/GaN along with a very low density of fixed bulk and interfacial charges. Conductance measurements on HfO2/GaN MOSCAPs reveal an interface trap state continuum with a density of 9.37x1012 eV-1cm-2 centered at 0.48 eV below EC. The forward and reverse current densities are shown to be governed by Fowler-Nordheim tu…
The degradation mechanisms of AlGaN/GaN HEMTs adopting Fe and C co-doping, with high and low carbon doping concentration were investigated by means of hot-electron step stress and 24 hours stress tests. Firstly, DC and EL characterization at room temperature are summarized, then the parametric evolution during hot-electron step stress tests at the semi-on state was compared, the assumption for the degradation mechanism is that hot-electrons activated the pre-existing traps in the buffer, attenuate the electric field in the gate drain access region and damaging the gate contact, the parametric …
In this work, we studied the gate breakdown mechanisms of p-GaN gate AlGaN/GaN HEMTs by a novel multiple-gate-sweep-based method. For the first time, three different breakdown mechanisms were observed and identified separately in the same devices: the metal/p-GaN junction breakdown, the p-GaN/AlGaN/GaN junction breakdown, and the passivation related breakdown. This method is an effective method to determine the breakdown mechanisms. The different BD mechanisms were further confirmed by scanning electron microscopy (SEM). Finally, the temperature dependences of the three BD mechanisms were meas…
The effect of a two dimensional (2D) graphene layer (GL) on top of the silicon nitride (SiN) passivation layer of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) has been systematically analyzed. Results showed that in the devices without the GL, the maximum drain current density (I_D,max) and the maximum transconductance (g_m,max) decreased gradually as the mist exposure time increased, up to 23% and 10%, respectively. Moreover, the gate lag ratio (GLR) increased around 10% during mist exposure. In contrast, devices with a GL showed a robust behavior and…
In this work, the threshold voltage instability of normally-off p-GaN high electron mobility transistors (HEMTs) has been investigated by monitoring the gate current density during device on-state. The origin of the gate current variations under stress has been ascribed to charge trapping occurring at the different interfaces in the metal/p-GaN/AlGaN/GaN system. In particular, depending on the stress bias level, electrons (VG < 6 V) or holes (VG > 6 V) are trapped, causing a positive or negative threshold voltage shift {DVTH, respectively. By monitoring the gate current variations at different…
We present a method to obtain quantitative profiles of surface state charge density and monitor its dynamics under various stress conditions in high electron mobility transistor (HEMT) devices. The method employs an optical spectroscopy of the channel current at various bias conditions. We test the method on a classical AlGaN/GaN HEMT structure. To analyze the results, we propose a model, according to which the energy distribution of the surface charge density may be obtained from the derivative of the channel photocurrent. The proposed method is applied to fully fabricated transistors and can…
O2-plamsa-based digital etching of Al0.25Ga0.75N with a 0.8 nm AlN spacer on GaN was investigated. At 40 W RF bias power and 40 sccm oxygen flow, the etch depth of Al0.25Ga0.75N was 5.7 nm per cycle. The 0.8 nm AlN spacer layer acted as an etch-stop layer in 3 cycles. The surface roughness improved to 0.33 nm after 7 digital etch cycles. Compared to the dry etch only approach, this technique causes less damages. It was shown to be effective in precisely controlling the AlGaN etch depth required for recessed-AlGaN HEMTs.
We report on the demonstration of a deep sub-micron normally-off AlGaN/GaN HEMT with high on-current and high threshold voltage (VTH). The high-performance device was realized by utilizing a gate recess with length and depth of 200 nm and 124 nm respectively. The recess etched region had a roughness of 0.7 nm. Various recess etch depths and dielectric annealing conditions were used to tune the VTH. The optimized device exhibited on-current and VTH of 500 mA/mm and 5 V respectively. The measured breakdown characteristics of the devices and their limitations were investigated using 2D-TCAD devic…
An ultraviolet (UV) photodetector employing the two-dimensional electron gas (2DEG) formed at the AlGaN/GaN interface as an interdigitated transducer (IDT) is characterized under optical stimulus. The 2DEG-IDT photodetector exhibits a record high normalized photocurrent-to-dark current ratio (NPDR, $6\times10^{14}$). In addition, we observe a high responsivity ($7,800$ A/W) and ultraviolet-visible rejection-ratio ($10^{6}$), among the highest reported values for any GaN photodetector architecture. We propose a gain mechanism to explain the high responsivity of this device architecture, which c…
Recently High Electron Mobility Transistor (HEMT) inspired III-V electro-optic modulator topologies were proposed for realizing high speed electro-optic modulators leveraging plasma dispersion effect due to the 2D Electron Gas (2DEG) present at the III-V heterostructure interface. The 2DEG is highly confined at the interface, extending to very low depths in the bulk ($\approx$10nm) and therefore has limited spatial overlap with the optical mode. In this paper, we propose a novel modulator design to boost the 2DEG-light interaction, wherein the HEMT is embedded within a high contrast grating (H…
In this paper, we report the use of lanthanum (La) in S/D contacts of GaN HEMTs, achieving 0.97 Ohm-mm contact resistance without S/D recess. The HEMTs show well-behaved electrical characteristics and satisfactory reliability. Our studies show that La, a CMOS compatible metal, is promising to lower GaN HEMT S/D contact resistance. La's low work function (3.5 eV) is beneficial for reducing the barrier between the metals and GaN. The Ohmic contact formation mechanism involved was shown to be different from conventional Ti/Al films. Spherical-shaped high-La regions formed near the surface during …
Novel devices such as tunneling field-effect transistors (FETs) and ferroelectric FETs have been demonstrated to break the subthreshold swing (SS) limit with sub-60 mV/decade switching for further low voltage/low power applications. In this paper, SS of sub-60 mV/dec was firstly observed in InAlN/GaN high electron mobility transistors (HMETs): an average SS of 30 mV/dec over three orders of magnitude in drain-source (Ids) and a minimum point-by-point SS of 15 mV/dec were achieved in the InAlN/GaN HEMTs with gate length (Lg) of 40 nm. It is found that SS decreases with drain-source voltage (Vds…
III-V heterostructure based high electron mobility transistors (HEMTs) offer superior performance as compared to CMOS silicon transistors owing to the high mobility in the 2D electron gas (2DEG) channel at the heterostructure interface. Gallium nitride (GaN) based HEMTs are also suitable for high power and high temperature applications. GaN has a rich offering of material properties spanning domains of nonlinear optics, piezoelectric micro-electro-mechanical systems (MEMS), and monolithic microwave integrated circuits (MMICs). In this paper, we propose HEMT inspired III-V electro-optic modulat…
We present an extensive analysis of the trapping processes induced by drain bias stress in AlGaN/GaN high-electron-mobility transistors (HEMTs) with p-GaN gate. We demonstrate that: (i) with increasing drain stress, pulsed I-V and VTH measurements shown an initial positive VTH variation and an increase in RON then, for drain voltages >100 V, VTH is stable and the RON shows a partial recovery. (ii) At moderate voltages, VTH instability is related to trapping at the gate stack, due to residual negative charge left behind by the holes that leave the p-GaN layer through the Schottky gate contact a…
The emerging wide bandgap BAlN alloys have potentials for improved III-nitride power devices including high electron mobility transistor (HEMT). Yet few relevant studies have been carried. In this work, we have investigated the use of the B0.14Al0.86N alloy as part or entirety of the interlayer between the GaN buffer and the AlGaN barrier in the conventional GaN-based high electron mobility transistor (HEMT). The numerical results show considerable improvement of the two-dimensional electron gas (2DEG) concentration with small 2DEG leakage into the ternary layer by replacing the conventional A…
Localized residual stress and elastic strain concentrations in microelectronic devices often affect the electronic performance, resistance to thermomechanical damage, and, likely, radiation tolerance. A primary challenge for characterization of these concentrations is that they exist over sub-$μ$m length-scales, precluding their characterization by more traditional residual stress measurement techniques. Here we demonstrate the use of synchrotron X-ray -based differential aperture X-ray microscopy (DAXM) as a viable, non-destructive means to characterize these stress and strain concentrations …
Central Electronics Engineering Research Institute（中央电子工程研究所）；Academy of Scientific and Innovative Research（科学与创新研究院）
This letter proposes a novel deep learning framework (DLF) that addresses two major hurdles in the adoption of deep learning techniques for solving physics-based problems: 1) requirement of the large dataset for training the DL model, 2) consistency of the DL model with the physics of the phenomenon. The framework is generic in nature and can be applied to model a phenomenon from other fields of research too as long as its behaviour is known. To demonstrate the technique, a semi-supervised physics guided neural network (SPGNN) has been developed that predicts I-V characteristics of a gallium n…
