High Electron Mobility Transistor Wafer Research Articles

A Pseudo‐Junction Barrier Schottky Diode in p‐GaN/AlGaN/GaN High Electron Mobility Transistor Epitaxial Layers

This work investigates a pseudo‐junction barrier Schottky (pseudo‐JBS) diode that is created by placing an AlGaN/GaN Schottky diode in parallel with a p‐GaN junction on the same epitaxial p‐GaN gate AlGaN/GaN high electron mobility transistor (HEMT) wafer. This pseudo‐JBS diode employs the two‐dimentional electron gas to increase the operation current, thus reducing the on‐resistance with high blocking voltage. The fabricated pseudo‐JBS diode with anode‐to‐cathode lengths (LAC) of 10 μm shows a turn‐on voltage of 1.05 V, a minimum specific on‐resistance (RON,MIN) of 2.53 mΩ cm2, and blocking voltage of 1112 V yielding an excellent Baliga's figure of merit of 488.7 MW cm−2 on the same epitaxial p‐GaN/AlGaN/GaN HEMT wafer. This study provides a promising substitute for Schottky barrier diodes without requiring extra p‐GaN layer design.

Van der Waals Heterostructure of Hexagonal Boron Nitride with an AlGaN/GaN Epitaxial Wafer for High-Performance Radio Frequency Applications.

While two-dimensional (2D) hexagonal boron nitride (h-BN) is emerging as an atomically thin and dangling bond-free insulating layer for next-generation electronics and optoelectronics, its practical implementation into miniaturized integrated circuits has been significantly limited due to difficulties in large-scale growth directly on epitaxial semiconductor wafers. Herein, the realization of a wafer-scale h-BN van der Waals heterostructure with a 2 in. AlGaN/GaN high-electron mobility transistor (HEMT) wafer using metal-organic chemical vapor deposition is presented. The combination of state-of-the-art microscopic and spectroscopic analyses and theoretical calculations reveals that the heterointerface between ∼2.5 nm-thick h-BN and AlGaN layers is atomically sharp and exhibits a very weak van der Waals interaction without formation of a ternary or quaternary alloy that can induce undesired degradation of device performance. The fabricated AlGaN/GaN HEMT with h-BN shows very promising performance including a cutoff frequency (fT) and maximum oscillation frequency (fMAX) as high as 28 and 88 GHz, respectively, enabled by an effective passivation of surface defects on the HEMT wafer to deliver accurate information with minimized power loss. These findings pave the way for practical implementation of 2D materials integrated with conventional microelectronic devices and the realization of future all-2D electronics.

Determination of Suitable Indicators of AlGaN/GaN HEMT Wafer Quality Based on Wafer Test and Device Characteristics

This study investigates various tests on AlGaN/GaN high electron mobility transistor (HEMT) wafers, including photoluminescence spectroscopy, secondary ion mass spectroscopy, X‐ray diffraction (XRD), and Hall measurement. The AlGaN/GaN HEMT wafers are grown on low‐resistivity Si substrates with various growth conditions for the buffer and channel layers. Characteristics of AlGaN/GaN HEMTs including drain lag, dynamic RON, and current transients were measured and correlated with the results from the wafer level tests. Results indicate that epitaxial wafers with low yellow luminescence (YL) to band edge (BE) and blue luminescence (BL) to BE ratios as well as a low carbon concentration but a similar low full width at half maximum of XRD profiles can result in devices with significant suppression of current collapse and the same on‐state device characteristics. Therefore, both YL/BE and BL/BE values combined with the carbon concentration in wafer level tests are suitable indicators for estimating device performance.

Heterogeneously Integrated W-Band Downconverter

We report a heterogeneously integrated W-band downconverter, consisting of a low noise amplifier (LNA) and a star mixer. An LNA is realized in a 0.1- $\mu \text{m}$ InP high-electron-mobility transistor (HEMT) technology and features the noise figure of ~2.5 dB and gain ≥25 dB at W-band. Star mixer is realized in four-layer interconnect InP heterojunction bipolar transistor (HBT) and diode process. A novel design eliminates electrically large diode ring by utilizing a multimetal configuration. Mixer chiplet is integrated into the LNA carrier wafer using heterogeneous integration, which offers electrically short connection between two technologies. Heterogeneously integrated interconnect or transition has measured a loss of ~0.8 dB up to 96 GHz. Integrated W-band downconverter has measured the conversion gain ≥0 dB from 87 to 100 GHz. This is a first reported integration of InP HBT chiplets into the InP HEMT wafer using heterogeneous integration, as well as first reported a W-band heterogeneously integrated downconverter.

Ultra‐thin barrier quaternary InAlGaN HEMTs with state of the art sheet resistance

AbstractWe report transport properties measured from quaternary barrier InAlGaN high electron mobility transistor wafers on SiC substrates. With similar barrier thicknesses, higher mobility and sheet charge density were both demonstrated by a strained barrier quaternary In0.07Al0.75Ga0.18N HEMT comparing to a ternary In0.17Al0.83N HEMT with lattice matched barrier to the GaN buffer. With 1 nm AlN interlayer, sheet resistances of 218 Ω/□ and 228 Ω/□ were obtained from 4.8 nm and 4.4 nm barrier structures, respectively. Both structures also show excellent electron motilities. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectroscopic photo I–V diagnostics of nitride‐based high electron mobility transistor structures on Si wafers

A simple and novel spectroscopic photo I–V method of diagnosing the homogeneity of electrically-active defect distribution in the large area AlGaN/GaN HEMT (high electron mobility transistor) epi-structure grown on 6-inch silicon wafers is reported. It is of utmost importance to produce the HEMT epi-structure electrically homogeneous across the wafer if devices with uniform electrical characteristics are to be constructed. AlGaN/GaN HEMT epi structures were grown on a silicon substrate via metal–organic chemical vapour deposition. An array of circular semi-transparent Ni Schottky contacts was prepared on top of the diced AlGaN/GaN HEMT structure substrates, which were selected from different locations of the 6-inch wafer. The information of the electrical homogeneity across the wafer was elucidated from the spectral dependences of the I–V characteristics collected from different locations of the AlGaN/GaN HEMT wafer. It is successfully demonstrated that the proposed spectroscopic photo I–V measurement technique can be employed to diagnose electrical homogeneity of the electrically-active defect distribution in the AlGaN/GaN HEMT epi structure constructed on Si with minimum sample preparation steps.

Tunable two-dimensional plasmon resonances in an InGaAs/InP high electron mobility transistor

Voltage-tunable plasmon resonances in the two-dimensional electron gas (2DEG) of a high electron mobility transistor (HEMT) fabricated from the InGaAs/InP materials system are reported. The device was fabricated from a commercial HEMT wafer by depositing source and drain contacts using standard photolithography and a semitransparent gate contact that consisted of a 0.5 μm period transmission grating formed by electron-beam lithography. Narrow-band resonant absorption of terahertz radiation was observed in transmission in the frequency range of 10–50 cm−1. The resonance frequency depends on the gate-tuned sheet charge density of the 2DEG. The observed separation of resonance fundamental from its harmonics and their shift with gate bias are compared with theory.

An internally-matched GaN HEMTs device with 45.2 W at 8 GHz for X-band application

Optimized AlGaN/AlN/GaN high electron mobility transistor (HEMT) with high mobility GaN channel layer structures were grown on 2-in. diameter semi-insulating 6H–SiC substrates by MOCVD. The 2-in. diameter GaN HEMT wafer exhibited a low average sheet resistance of 261.9 Ω/square, with the resistance un-uniformity as low as 2.23%. Atomic force microscopy measurements revealed a smooth AlGaN surface whose root-mean-square roughness is 0.281 nm for a scan area of 5 × 5 μm. For the single-cell HEMTs device of 2.5-mm gate width fabricated using the materials, a maximum drain current density of 1.31 A/mm, an extrinsic transconductance of 450 mS/mm, a current gain cutoff frequency of 24 GHz and a maximum frequency of oscillation 54 GHz were achieved. The four-cell internally-matched GaN HEMTs device with 10-mm total gate width demonstrated a very high output power of 45.2 W at 8 GHz under the condition of continuous-wave (CW), with a power added efficiency of 32.0% and power gain of 6.2 dB. To our best knowledge, the achieved output power of internally-matched devices are the state-of-the-art result ever reported for X-band GaN-based HEMTs.

Surface strain and its impact on the electrical resistivity of GaN channel in AlGaN/GaN high electron mobility transistor

Localized strain in AlGaN/GaN high electron mobility transistor (HEMT) device structures was studied by high resolution x-ray diffraction and rocking curve measurements, and the results were compared with the corresponding channel sheet resistance measurements. The map of in-plane tensile strain on the HEMT wafer showed a near one-to-one correspondence with the electrical resistivity. The in-plane strain variation in the range of (2.295–3.539)×10−4 resulted in a corresponding sheet resistance variation between 345 and 411 Ω/◻.

Steady state and transient behavior of currents in AlGaN∕GaN planar Schottky diodes and mechanism of current collapse

To get information on the current collapse mechanism under gate bias stress in AlGaN∕GaN heterostructure field effect transistors, this article investigates the steady state and transient behavior of current in a planar Schottky metal contact formed on a standard AlGaN∕GaN high electron mobility transistor wafer. Schottky contacts with reduced reverse leakage currents were prepared by using an oxygen gettering process, and their electrical characteristics were studied by current-voltage, capacitance-voltage, and current-time measurements at various temperatures. When the voltage pulse was applied into the pinch-off region, an excess current flew, showing very slow nonexponential transients covering six orders of magnitude of time from millisecconds to thousand seconds. Turn-off transients were also slow and highly nonexponential. The current transients are shown to be due to charging and discharging of the virtual gate capacitor with the electrons in and out of surface trapping states where the rate limiting process is the hopping process of electrons. The process can be described by a dispersive hopping transport, leading to charging behavior with a stretched exponential dependence on time and discharging behavior with power law dependence on time. Theoretical formulas showed good agreements with experiments, and provide ample description of the transients processes directly related to the current collapse.

Surface-induced large side-gating phenomenon in GaAs quantum wire transistors and its removal by surface passivation using Si interface control layer

Side-gating behaviors of GaAs-based quantum wire transistors (QWRTr’s) were investigated. Using AlGaAs∕GaAs high electron mobility transistor wafer, the QWRTr was fabricated with a nanosized side gate beside the nanowire. Anomalous large side-gating effect was found for the QWRTr. Experiments showed that the large side-gating effect was owing to the strong surface Fermi level pinning around the nanowire, which is caused by a thin layer of deep traps located at the surface. Then, Si interface control layer passivation technology was performed to remove the large side gating.

1-mm gate periphery AlGaN/AlN/GaN HEMTs on SiC with output power of 9.39 W at 8 GHz

AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with high mobility GaN channel layer were grown on 50 mm diameter semi-insulating (SI) 6H-SiC substrates by metalorganic chemical vapor deposition and large periphery HEMT devices were fabricated and characterized. High two-dimensional electron gas mobility of 2215 cm 2/V s at room temperature with sheet electron concentration of 1.044 × 10 13/cm 2 was achieved. The 50 mm diameter HEMT wafer exhibited a low average sheet resistance of 251.0 Ω/square, with the resistance uniformity of 2.02%. Atomic force microscopy measurements revealed a smooth AlGaN surface with a root-mean-square roughness of 0.27 nm for a scan area of 5 μm × 5 μm. The 1-mm gate width devices fabricated using the materials demonstrated a very high continuous wave output power of 9.39 W at 8 GHz, with a power added efficiency of 46.2% and power gain of 7.54 dB. A maximum drain current density of 1300 mA/mm, an extrinsic transconductance of 382 mS/mm, a current gain cutoff frequency of 31 GHz and a maximum frequency of oscillation 60 GHz were also achieved in the same devices.

AlGaN/AlN/GaN/SiC HEMT structure with high mobility GaN thin layer as channel grown by MOCVD

Enhancement of the electrical properties in an AlGaN/GaN high electron mobility transistor (HEMT) structures was demonstrated by employing the combination of a high mobility GaN channel layer and an AlN interlayer. The structures were grown on 50 mm semi-insulating (SI) 6H-SiC substrates by metalorganic chemical vapor deposition (MOCVD). The room temperature (RT) two-dimensional electron gas (2DEG) mobility was as high as 2215 cm 2/V s, with a 2DEG concentration of 1.044×10 13 cm −2. The 50 mm HEMT wafer exhibited a low average sheet resistance of 251.0 Ω/square, with a resistance uniformity of 2.02%. The 0.35 μm gate length HEMT devices based on this material structure, exhibited a maximum drain current density of 1300 mA/mm, a maximum extrinsic transconductance of 314 mS/mm, a current gain cut-off frequency of 28 GHz and a maximum oscillation frequency of 60 GHz. The maximum output power density of 4.10 W/mm was achieved at 8 GHz, with a power gain of 6.13 dB and a power added efficiency (PAE) of 33.6%.

Influence of AlN interfacial layer on electrical properties of high-Al-content Al0.45Ga0.55N/GaN HEMT structure

Unintentionally doped high-Al-content Al0.45Ga0.55N/GaN high electron mobility transistor (HEMT) structures with and without AlN interfacial layer were grown by metal–organic chemical vapor deposition (MOCVD) on two-inch sapphire substrates. The effects of AlN interfacial layer on the electrical properties were investigated. At 300K, high two-dimensional electron gas (2DEG) density of 1.66×1013cm−2 and high electron mobility of 1346cm2V−1s−1 were obtained for the high Al content HEMT structure with a 1nm AlN interfacial layer, consistent with the low average sheet resistance of 287Ω/sq. The comparison of HEMT wafers with and without AlN interfacial layer shows that high Al content AlGaN/AlN/GaN heterostructures are potential in improving the electrical properties of HEMT structures and the device performances.

Characterization of AlInAs/InGaAs High Electron Mobility Transistor Wafers Treated with Remote Phosphine Plasma

Surface modification of AlInAs/InGaAs high electron mobility transistor (HEMT) wafers has been investigated to suppress the diffusion of fluorine (F) atoms into an n-AlInAs layer. The surface of the HEMT wafer is phosphidized using remote phosphine (PH3) plasma. Secondary ion mass spectroscopy analysis reveals that F diffusion is suppressed even after annealing at 400°C for 15 min for the phosphidized sample. It is also demonstrated by Hall measurements that no significant reduction in the two-dimensional electron density occurs due to annealing. Formation of the modification layer containing phosphorus (P) atoms is shown by X-ray photoelectron spectroscopy analysis. The PH3 plasma treatment is effective in suppressing the diffusion of F atoms into the n-AlInAs layer.

Photoreflectance Characterization of a Channel Layer of InAlAs/InGaAs High Electron Mobility Transistor Wafers

Using room-temperature (RT) -photoreflectance (PR), we have succeeded in characterizing InGaAs channel layers of InAlAs/InGaAs high electron mobility transistors (HEMTs). The relationship between PR spectra and sheet carrier density (Ns) is discussed. The valleys observed in the PR spectra correspond to the transitions between the quantized levels in the valence and conduction bands. A valley shift to the lower energy side is observed with increasing Ns, which corresponds to the shift of the intersubband energies. The calculation of the intersubband energies supports the results of the PR measurements. PR spectroscopy is quite promising for the non-destructive characterization of Ns of InAlAs/InGaAs HEMTs at RT.

Simulations of HEMT DC drain current and 1 to 50 GHz S-parameters as a function of gate bias

The usefulness over an extended range of a high-electron-mobility transistor (HEMT) model previously validated for a 1-25-GHz S-parameter model is shown. Experimental and simulation results for the DC drain current and 1-50-GHz S-parameters of a pseudomorphic 0.32- mu m gate AlGaAs-InGaAs-GaAs HEMT are presented. The model predicts the device's DC current and S-parameters as functions of the applied gate bias with good accuracy. The core of the model is directly dependent on the HEMT wafer structure and the physical gate length. As part of the modeling procedure, a value of (1.77+or-0.07)*10/sup 5/ m-s/sup -1/ is found, confirming the results of other research, for the electron velocity in undoped pseudomorphic In/sub 0.15/Ga/sub 0.85/As under approximately=0.3- mu m gates. >