Chia-Song Wu

Characteristics of a In/sub 0.52/(Al/sub x/Ga/sub 1-x/)/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As(0/spl les/x/spl les/1) heterojunction and its application on HEMT's

The quaternary In/sub 0.52/(Al/sub x/Ga/sub 1-x/)/sub 0.48/As compound on InP substrates is an important material for use in optoelectronic and microwave devices. We systematically investigated the electrical properties of quaternary In/sub 0.52/(Al/sub x/Ga/sub 1-x/)/sub 0.48/As layers, and found a 10% addition of Ga atoms into the InAlAs layer improves the Schottky diode performance. The energy bandgap (E/sub g/) for the In/sub 0.52/(Al/sub x/Ga/sub 1-x/)/sub 0.48/As layer was (0.806+0.711x) eV, and the associated conduction-band discontinuity (/spl Delta/E/sub c/), in the InAlGaAs/In/sub 0.53/Ga/sub 0.47/As heterojunction, was around (0.68/spl plusmn/0.01)/spl Delta/E/sub g/. Using this high quality In/sub 0.52/(Al/sub 0.9/Ga/sub 0.1/)/sub 0.48/As layer in the Schottky and buffer layers, we obtained quaternary In/sub 0.52/(Al/sub 0.9/Ga/sub 0.1/)/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As HEMTs. This quaternary HEMT revealed excellent dc and microwave characteristics. In comparison with the conventional InAlAs/InGaAs HEMTs, quaternary HEMTs demonstrated improved sidegating and device reliability.

Characteristics of In0.3Ga0.7As/In0.29Al0.71As Heterostructures Grown on GaAs Using InAlAs Buffers

Device quality In0.29Al0.71As and In0.3Ga0.7As epilayers have been successfully grown on GaAs substrates using a carefully designed Inx Al1-x As multistage strain-relaxed buffer. Cross-sectional transmission electron microscopy has shown that the misfit dislocations are confined in the lower regions of the metamorphic buffer layer. The Hall electron mobility of the modulation doped structure grown on the InAlAs buffer was 6160 and 25379 cm2/V s with sheet carrier densities of 1.9×1012 and 1.8×1012 cm-2 at 300 and 77 K, respectively. The excellent characteristics of the field-effect transistors fabricated on this structure have indicated its potential for practical applications.

GaAs-based In0.29 Al0.71As/In0.3Ga0.7As high-electron mobility transistors

In0.29Al0.71As/In0.3Ga0.7 As heterostructures grown on GaAs substrates with a step-graded metamorphic InxGa1−x As buffer were characterized. Cross-sectional TEM micrographs revealed that an unstrained and dislocation-free In0.3Ga0.7As layer used as a buffer can be obtained. A 0.6-μm-long gate HEMT based on this heterostructure demonstrated a gm of 230 mS/mm, an fT of 23 GHz, and an fmax of 73 GHz.

Double-heterojunction pseudomorphic AlGaAs/In0.15Ga0.85As HEMT and its short-channel effects

AlGaAs/In0.15Ga0.85As double-heterojunction pseudimorphic high electron mobility transistors (DH-PHEMTs) were fabricated by the deep-UV lithographic technique. 0.6 μm gate-length devices demonstrated a full channel current of 300 mA/mm at 300 K and 420 mA/mm at 77 K respectively, which is 1.5 times higher than that of single-heterojunction (SH) PHEMTs[1]. D.C. I-V characteristics showed a peak extrinsic transconductance of 230 and 330 mS/mm at 300 and 77 K, respectively. Microwave characteristics revealed a current gain cutoff frequency (fT) of 16 GHz and a maximum oscillation frequency (fmax) of 61 GHz at 300 K. Due to a better carrier confinement in this double-heterostructure, short channel effects are less significant as compared to the single-heterostructure HEMTs.

In/sub 0.52/(Al/sub 0.9/Ga/sub 0.1/)/sub 0.48/As/In/sub 0.53/Ga/sub 0.4/

In this report, we try to improve the quality of the In/sub 0.52/Al/sub 0.48/As layer, by substituting 10% of Al atoms with Ga atoms, and forming a In/sub 0.52/(Al/sub 0.9/Ga/sub 0.1/)/sub 0.48/As quaternary (Q) layer. This quaternary InAlGaAs layer is used as the Schottky and buffer layers in HEMT structures. With the incorporation of Ga atoms, the alloy scattering can be eliminated due to the higher surface mobility of Ga atoms during MBE growth. This composition is chosen based on the consideration of maintaining a good Schottky gate performance, where a reasonably high bandgap Schottky layer is necessary. Since it is expected that this InAlGaAs Q-layer can improve the device duality, we particularly focus on reliability and sidegate testing for InAlGaAs Q-HEMTs. For comparison, the results obtained from the conventional InP-HEMTs are also included.

d7As HEMTs on InP substrates

The unstrained or the so-called metamorphic In/sub 0.29/Al/sub 0.71/As/In/sub 0.3/Ga/sub 0.7/As heterostructure FETs (HFETs), including HEMTs and DCFETs, have been fabricated on GaAs substrates by using a compositionally step-graded buffer design. A peak extrinsic DC transconductance (gm) of 230 mS/mm and saturation current density of 385 mA/mm were measured from a HEMTs device with 0.6 /spl mu/m-long gate length. This device also shows a current-gain cut-off frequence (f/sub T/)of 23 GHz and a maximum available, gain cut-off frequency (f/sub max/) of 73 GHz. Based on the DCFETs, a g/sub m/ of 220 mS/mm and a full channel current of 400 mA/mm were achieved for a 1/spl mu/m-long gate device. Also, the RF performance of f/sub T/=22 GHz and f/sub max/=51 GHz have been obtained.