n + -GaAs / p + -InAlGaP / n + -InAlGaP Camel-Gate High-Electron Mobility Transistors

Abstract

This investigation proposes InAlGaP/InGaAs camel-gate high-electron mobility transistors with inverted ␦-doping layers ͑CAM-HEMTs͒. CAM-HEMTs with various gate metals, including Au, Pt/Au, Ti/Au, and Ni/Au, are investigated. The CAM-HEMT with the Ni/Au gate metal exhibits the benefits of a large gate voltage swing ͑3.6 V͒, a high two-terminal gate-source breakdown voltage ͑Ͼ20 V͒, no bell-shaped gate current and temperature-insensitive threshold voltages. These characteristics are attributable to the inverted ␦-doping layer, the large conduction-band discontinuity of the InAlGaP/InGaAs heterojunction, the large bandgap of InAlGaP and the high camel-gate barrier with the Ni/Au gate metal.Over the past several years, InGaP/InGaAs high-electron mobility transistors ͑HEMTs͒ have become one of the most important semiconductor devices used in microwave applications. 1-3 Several structures have been reported to improve the breakdown voltage of the heterostructure field-effect transistors ͑HFETs͒ without decreasing the current drivability, such as buried gate HFETs, 4 metalinsulator-semiconductor FETs, 5 and camel-gate FETs ͑CAMFETs͒. 6-10 In particular, the CAMFET provides several advantages, such as ͑i͒ the elimination of metallurgical difficulties associated with metal-semiconductor contacts; ͑ii͒ the relative ease of adjustment of the built-in voltage, and ͑iii͒ the potential for improving reliability at high temperatures. For high power applications, the device should have a high breakdown voltages and high current driving capability. The driving currents are directly related to the sheet charge density in the channel. An effective way to increase the sheet charge density is to use material systems with a large conduction-band discontinuity. [10][11][12][13][14][15] In principle, a larger conductionband discontinuity corresponds to a larger sheet charge density, so the current driving capability is greater. The larger conduction-band discontinuity in HEMTs also reduces the output conductance and the real space transfer, improving the performance of the devices. Our previous studies demonstrated the use of alternative InAlAsSb/InP 14,15 and InAlGaP/GaAs 16 materials systems used in microwave devices. Recently, Liu et al. presented a series of GaAs/InGaP CAMFETs. 8,10 However, no study has focused on GaAs/InAlGaP CAMFETs. Therefore, this work presents high-electron mobility transistors with the quaternary camel-gate and inverted ␦-doping layer ͑CAM-HEMTs͒. The n + -GaAs/p + -InAlGaP/n + -InAlGaP camel gate is employed to replace the GaAs homojunction camel gate, 6-8 the GaAs/AlGaAs heterojunction camel gate, 6,7 the GaAs/InGaP heterojunction camel gate, 9,10 and the conventionally used Schottky gate. 3,11,14 The highbarrier gate can effectively prevent electron injection into the channel. The good carrier confinement in the InAlGaP/InGaAs/InAlGaP heterostructure channel also reduces the substrate leakage current at elevated temperatures. The experimental data demonstrate the excellent output characteristics of the CAM...

Simulation Study of the Correlation between Structure and Conductivity in Stretched Nafion

“…Cable et al 8 , for example, stretched Nafion and found the proton conductivity to be higher in the plane of the membrane than normal to it. A slightly different result was found by Lin et al 9 , who noted little change in transverse conductivity on stretching, but found an improved fuel cell performance, as compared to Nafion 117 and unstretched recast Nafion, as a consequence of a lowered methanol permeation rate. In a related experiment, Elabd et al 10 measured the conductivities of an ionic block copolymer, and observed appreciable anosotropy.…”

Improved InAlGaP-based heterostructure field-effect transistors

“…The InAlGaP/GaAs HFET exhibits the more favourable g m , I max and BV gs because the InAlGaP/GaAs heterojunction has a high E C and InAlGaP has a large band gap. Additionally, the examined InAlGaP/GaAs HFET exhibits better g m and I max values than the other HEMTs [3,4,8,[16][17][18][19], even though this InAlGaP/GaAs HFET has a longer gate length. Moreover, the high-frequency characteristics are measured by an HP-8510C network analyser.…”

“…However, because InAlGaP/GaAs heterostructures have the advantages of high E C and high E g , the n-InAlGaP/GaAs HFET is also investigated. Experimental results demonstrate that both these improved structures have better dc characteristics than the previously reported HFETs [1][2][3][4][5][6][7][8][17][18][19]].…”

“…Unfortunately, the two-dimensional electron gas (2DEG) densities of the InGaP HEMTs remain limited by their relatively small E C , which, in turn, limits their currentdriving capability [1][2][3][4][5][6][7]. The In 0.5 (Al x Ga 1−x ) 0.5 P/GaAs heterojunctions are excellent alternative materials for use in electronic and optoelectronic devices [8]. The In 0.5 (Al x Ga 1−x ) 0.5 P/GaAs heterojunction with x 0.2 has a larger E C ( 0.25 eV) than the Al 0.23 Ga 0.77 As/GaAs (0.19 eV) or In 0.5 Ga 0.5 P/GaAs heterojunction.…”

Investigation of InGaP/InGaAs n- and p-channel pseudomorphic modulation-doped field effect transistors with high gate turn-on voltages

“…An alternative structure to the junction FET is the n + /p + /n camel-gate field effect transistor (CAMFET), in which high potential barrier heights and gate voltage swings have been achieved [9][10][11][12]. The basic structures of a CAMFET consist of an n + -doped cap layer, a relatively thin p + -doped layer, and an active n-type doped channel.…”