Metamorphic High Electron Mobility Research Articles

LG = 20 nm High Performance GaAs Substrate Based Metamorphic Metal Oxide Semiconductor High Electron Mobility Transistor for Next Generation High Speed Low Power Applications

<i>L</i>_G = 20 nm High Performance GaAs Substrate Based Metamorphic Metal Oxide Semiconductor High Electron Mobility Transistor for Next Generation High Speed Low Power Applications

Stability Investigation of Large Gate-Width Metamorphic High Electron-Mobility Transistors at Cryogenic Temperature

An investigation of metamorphic high electron mobility transistor stability at cryogenic temperature is presented in this paper. Unlike in the case of two-finger transistors, the measurements of cooled four-finger devices with large gate widths exhibit unstable behavior in the form of steps in the current–voltage characteristics, discontinuities in the transconductance, and reduced gain. This unstable behavior has hampered the reliable realization of low-noise amplifiers for cryogenic applications. We study different gate-width devices with a multiport transistor model, allowing the separation of gate and drain feeder structures from the active part of the transistor. The simulation reveals the presence of resonances in the frequency region of several hundreds of gigahertz. We demonstrate that the resonances disappear when an air bridge is placed across the fingers of the drain feeder structure, and confirm the stabilizing effect of the air bridge both on device and circuit level by cryogenic measurements.

Study of a MHEMT heterostructure with an In0.4Ga0.6As channel MBE-grown on a GaAs substrate using reciprocal space mapping

The crystallographic characteristics of the design elements of a metamorphic high-electron-mobility (MHEMT) heterostructure with an In0.4Ga0.6As channel are determined based on reciprocal space mapping. The heterostructure is grown by molecular beam epitaxy on the vicinal surface of a GaAs substrate with a deviation angle from the (001) plane of 2° and consists of a stepped metamorphic buffer containing six layers including an inverse step, a high-temperature buffer layer with constant composition, and active HEMT layers. The InAs content in the layers of the metamorphic buffer is varied from 0.1 to 0.48. Reciprocal space maps are constructed for the (004) symmetric reflection and (224)+ asymmetric reflection. It is found that the heterostructure layers are characterized both by a tilt angle relative to the plane of the (001) substrate and a rotation angle around the [001] axis. The tilt angle of the layer increases as the InAs concentration in the layer increases. It is shown that a high-temperature buffer layer of constant composition has the largest degree of relaxation compared with all other layers of the heterostructure.

Comprehensive Temperature-Dependent Studies of Metamorphic High Electron Mobility Transistors With Double and Single $\delta$-Doped Structures

The temperature-dependent characteristics of meta morphic high electron mobility transistors (MHEMTs) with double and single δ-doped structure are studied and demonstrated. Due to the use of double δ-doped sheets, the current density in the channel layer and two-dimensional electron gas could effectively be increased. The excellent turn-on voltage of 1.18 (0.80) V, max imum drain saturation current of 544 (524) mA/mm, maximum extrinsic transconductance of 361 (312) mS/mm, unity current gain cutoff frequency of 55.06 GHz, and maximum oscillation frequency of 129.17 GHz are obtained at 300 (510) K for a 0.6 × 100 μm2 gate dimension double δ-doped MHEMT. In addition, using wide-bandgap InAlAs Schottky, spacer, and buffer layers, the carrier confinement could significantly be improved at high temperature. Therefore, excellent thermal stability is achieved for double δ-doped MHEMT. The device with a double δ-doped structure exhibits a considerably low temperature coefficient on threshold voltage (∂Vth/∂T) of 0.06 mV/K when the temperature is increased from 330 to 510 K, which is superior to previous reports of related high electron mobility transistors.

Effects of Multigate-Feeding Structure on the Gate Resistance and RF Characteristics of 0.1-$\mu{\hbox{m}}$ Metamorphic High Electron-Mobility Transistors

We investigate the effects of a multigate-feeding structure on the gate resistance (Rg) and RF characteristics of the high electron-mobility transistors (HEMTs). In this structure, the increase of Rg with the gatewidth (W) is minimized; therefore, high maximum frequency of oscillation (fmax) is achieved. Various numbers of gate feedings (Ngf) using the air-bridge interconnections are adopted for fabricating the 0.1-mum depletion-mode metamorphic HEMTs. From these structures, we observe great reduction in Rg with the increase of Ngf, and their relationship is given by Rgprop 1/[2middot(Ngf-1)]2, where Ngf=2,3,4,...; on the other hand, the effects of Ngf on other small-signal parameters are negligible. Calculated cutoff frequency (fT) and fmax from the extracted small-signal parameters all show good agreement with the measurement results. fT is slightly decreased with the increase of Ngf due to the increase of gate-to-source capacitance. fmax is, however, greatly increased with Ngf, and this effect becomes greater at longer total gatewidth (W times number of gate fingers) . This is due to the smaller Rg at greater Ngf in the multigate-feeding structure. We propose that this gate-feeding structure provides a very effective way to suppress Rg and maximize fmax for the applications of the HEMTs with long W.

GaAs HEMT Reliability and Degradation Mechanisms after Long Term Stress Testing

AbstractGaAs based metamorphic and pseudomorphic high electron mobility transistors (HEMTs) under DC and thermal stress were studied. InAlAs/InGaAs MHEMTs grown on GaAs substrates were stressed at a drain voltage bias of 2.7V for 36 hours as well as thermally stressed at 250°C for 36 hours. Under both stress conditions, the drain current density decreased about 12.5%. The gate current, however, increased more after the thermal storage as opposed to DC bias. Reaction of the Ohmic contact with the underlying semiconductor was the main cause of degradation after thermal stressing. Transmission electron microscopy verified that gate sinking occurred in devices that underwent DC bias stressing. InGaAs pHEMTs that received a 1000 hour lifetime stress test from a commercial vendor showed similar degradation as virgin devices when stressed under DC bias for 24 hours. Virgin devices that were thermally stressed while undergoing DC bias showed minimal degradation up to 120°C, but exhibited catastrophic failure at 140°C.

Asymmetrically Recessed 50-nm Gate-Length Metamorphic High Electron-Mobility Transistor With Enhanced Gain Performance

We report the design, fabrication and characterization of ultrahigh gain metamorphic high electron-mobility transistors. In this letter, a high-yield 50-nm T-gate process was successfully developed and applied to epitaxial layers containing high indium mole fraction InGaAs channels grown on GaAs substrates. A unique gate recess process was adopted to significantly increase device gain by effectively suppressing output conductance and feedback capacitance. Coupled with extremely small 10 mum times 25 mum via holes on substrates thinned to 1 mil, we achieved a 13.5 dB maximum stable gain (MSG) at 110 GHz for a 30-mum gate-width device. To our knowledge, this is the highest gain performance reported for microwave high electron-mobility transistor devices of similar gate periphery at this frequency, and equivalent circuit modeling indicates that this device will operate at frequencies beyond 300 GHz.

InAlAs/InGaAs metamorphic low-noise HEMT

An In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As metamorphic low-noise high electron mobility transistor (HEMT) has been developed. A growth temperature by molecular beam epitaxy (MBE) and a thickness of a linearly graded InAlAs buffer layer have been optimized in order to reduce the density of lattice-misfit dislocation. Relatively high sheet electron density and mobility of 2.6/spl times/10/sup 12/ cm/sup -2/ and 9500 cm/sup 2//V sec at room temperature, respectively, are obtained. A 0.1-/spl mu/m-gate low-noise HEMT is fabricated using the developed epitaxial wafer A minimum noise figure of 0.48 dB with an associated gain of 14.2 dB has been obtained at 18 GHz.