Surface passivation of InGaP/InGaAs/GaAs pseudomorphic HEMTs with ultrathin GaS film

We report on the successful surface passivation of wide recess InGaP/InGaAs/GaAs pseudomorphic HEMTs with MBE-grown ultrathin GaS film (2 nm) employing a single precursor, tertiarybutyl-galliumsulfide-cubane ([(t-Bu)GaS]/sub 4/). At the recess length of 1.1 /spl mu/m, a GaS-passivated device with a 0.5-/spl mu/m gate length has the maximum transconductance (g/sub m max/) of 347 mS/mm, which is about 40% higher than that of 240 mS/mm for a device without GaS passivation. We found that one of the causes of an increased g/sub m max/ is the decrease of sheet resistance on the recessed surface because GaS passivation has reduced the depletion layer. Meanwhile, the two-terminal gate-to-drain reverse breakdown voltage (BV/sub gd/) was reduced after GaS passivation. The BV/sub gd/ is independent of the recess length between gate and drain (L/sub gd/) for GaS-passivated devices, unlike that for devices without GaS passivation. According to our calculation of the BV/sub gd/ involving the effects of impact ionization and the interface state, the BV/sub gd/ becomes almost independent of the L/sub gd/, when the interface state density (N/sub int/) is below 1/spl times/10/sup 12/ cm/sup -2/. Then, the calculated surface potential at the recess region is less than 0 eV. This result suggests that GaS passivation can remarkably reduce the N/sub int/ at the recess region.     

Double pulse doped InGaAs/AlGaAs/GaAs pseudomorphic high-electron-mobility transistor heterostructures

Double pulse doped (δ-doped) InGaAs/AlGaAs/GaAs pseudomorphic high-electron-mobility transistor (HEMT) heterostructures were grown by molecular-beam epitaxy using a multiwafer technological system. The room-temperature electron mobility was determined by the Hall method as 6550 and 6000 cm²/(V s) at sheet electron densities of 3.00 × 10¹² and 3.36 × 10¹² cm⁻², respectively. HEMT heterostructures fabricated in a single process feature high uniformity of structural and electrical characteristics over the entire area of wafers 76.2 mm in diameter and high reproducibility of characteristics from process to process.     

High performance pseudomorphic InGaP/InGaAs power HEMTs

Power transistors with a low d.c. supply voltage were demonstrated with pseudomorphic InGaP/In_0.2Ga_0.8As/GaAs heterostructure field effect transistors on GaAs substrates and 1 μm gate length technology. A current density of 200 mA mm⁻¹ and an extrinsic transconductance of 300 mS mm⁻¹ were exhibited on a 400 μm gate width process control monitor device. For a 1 cm gate width device measured at 850 MHz and V_ds = 1.3 V, state-of-the-art results, 57.4% for the PAE, 12.7 dB for the linear gain and 21.5 dBm for the output power, were obtained.     

Temperature dependence of high-frequency performance ofAlGaAs/InGaAs pseudomorphic HEMT's

High-frequency measurements of 1.5-μm gatelength AlGaAs/InGaAs pseudomorphic HEMTs have been performed at temperatures ranging from 77 to 463 K. A 28% increase and 27% decrease in f_T were observed by changing the temperature from 300 to 77 K and from 300 to 463 K, respectively. The effective saturation velocity evaluated from the total delay time, 1/2πf_T, versus reciprocal I_DS relation reveals almost the same temperature dependence as f_T. It is also shown that the temperature dependence is similar to that of calculated velocity at high electric fields but not to that at low fields. This suggests that the temperature dependence of the HEMT performance is determined by that of the saturation velocity in the channel     

InGaP/InGaAs metal-oxide-semiconductor pseudomorphic high-electron-mobility transistor with a liquid-phase-oxidized InGaP as gate dielectric

An InGaP/InGaAs metal-oxide-semiconductor pseudomorphic high-electron-mobility transistor (MOS-PHEMT) with a thin InGaP oxide layer as the gate dielectric is demonstrated. The MOS-PHEMT not only has the advantages of the MOS structure but also has the high-density, high-mobility 2DEG channel. The MOS-PHEMTs have larger gate swing voltages, lower gate leakage currents, and higher breakdown voltages than their counterpart PHEMTs have. Thus, the proposed MOS-PHEMT may be promising in power device applications.     

Ultralow-noise W-band pseudomorphic InGaAs HEMT's

Low-noise planar doped pseudomorphic (PM) InGaAs high-electron-mobility transistors (HEMTs) with a gate length of 0.1 μm for W-band operation are discussed. These devices feature a multiple-finger layout with air bridges interconnecting the sources to reduce gate resistance. The device exhibits a minimum noise figure of 2.5 dB with an associated gain of 4.7 dB at 92.5 GHz. This result demonstrates the feasibility of using PM InGaAs HEMTs for W-band low-noise receivers without the need for using lattice-matched InP HEMTs     

The study of δ-doped InGaP/InGaAs/GaAs pseudomorphic high electron mobility transistor

An enhancement-mode pseudomorphic high electron mobility transistor (E-mode pHEMT) with In_0.49Ga_0.51P/In_0.25Ga_0.75As/GaAs structure is studied in this paper. The two-dimensional device simulator, MEDICI, is used to solve the Poisson's equation and the electron/hole current continuity equations. An optimized δ-doped InGaP/InGaAs pHEMT structure is found to be superior to the conventional AlGaAs/InGaAs pHEMT. It reveals that the maximum drain-source current (I_DS) goes up to 1600 mA/mm and transconductance (G_m) is 2120 mS/mm.     

Monolithic V-band frequency converter chip set development using0.2 μm AlGaAs/InGaAs/GaAs pseudomorphic HEMT technology

Monolithic approaches of the development to V-band frequency converters have the advantages of lighter weight and lower cost over conventional hybrid approaches for high volume insertions into satellite communication systems. This paper presents the design, fabrication, and performance of a monolithic V-band frequency converter chip set using 0.2 μm AlGaAs/InGaAs/GaAs pseudomorphic HEMT technology. This chip set consists of three monolithic macrocells and a microcell: an upconverter, a downconverter, and a frequency multiplier for LO signal. A monolithic balanced amplifier microcell is also used to form the LO chain. Individual components, including amplifiers, mixer, and frequency doublers are also described. The superb measured results obtained from this chip set show great promise of the MMIC insertions for the system applications, and represent state-of-the-art performance of MMIC at this frequency     

Characteristics of InGaP/InGaAs pseudomorphic high electron mobility transistors with triple delta-doped sheets

Fundamental and insightful characteristics of InGaP/InGaAs double channel pseudomorphic high electron mobility transistors (DCPHEMTs) with graded and uniform triple δ-doped sheets are coomprehensively studied and demonstrated. To gain physical insight, band diagrams, carrier densities, and direct current characteristics of devices are compared and investigated based on the 2D semiconductor simulator, Atlas. Due to uniform carrier distribution and high electron density in the double InGaAs channel, the DCPHEMT with graded triple δ-doped sheets exhibits better transport properties, higher and linear transconductance, and better drain current capability as compared with the uniformly triple δ-doped counterpart. The DCPHEMT with graded triple δ-doped structure is fabricated and tested, and the experimental data are found to be in good agreement with simulated results.     

Trapped charge modulation: a new cause of instability inAlGaAs/InGaAs pseudomorphic HEMT's

A new degradation mechanism of PM-HEMT's subsequent to hot electron stress tests or high temperature storage tests is presented. A noticeable increase in drain-to-source current, I_DS, is observed after the tests. We show that this I_DS variation is slowly recoverable and is correlated with the presence of deep levels in the device. Stress tests cause a variation of trapped charge. Trapping of holes created by impact-ionization and/or thermally stimulated electron detrapping induce a variation of the net negative trapped charge, leading to a decrease in the threshold voltage, V_T and a consequent increase in I_DS. The correlation between g _mΔV_T and ΔI_DS clearly demonstrates that the variation of trapped charge induced by hot electron tests is localized under the gate     

Functional AlGaAs/GaAs heterostructure-emitter bipolar transistor with a pseudomorphic InGaAs/GaAs quantum-well base

A new functional AlGaAs/GaAs heterostructure-emitter bipolar transistor (HEBT) with a pseudomorphic InGaAs/GaAs quantum-well (QW) base structure is presented. Due to the insertion of an InGaAs QW between the emitter–base (E–B) junction, the valence band discontinuity can be enhanced. The excellent transistor characteristics including a high current gain of 280 and a low offset voltage of 100 mV are obtained. In addition, an interesting multiple S-shaped negative differential resistance (NDR) phenomenon is observed under the inverted operation mode. This may be attributed to an avalanche multiplication and sequential two-stage barrier lowering effect.     

MOCVD-grown broad area InGaAs/GaAs/InGaP laser diodes

A MOCVD technology for growth of InGaAs/GaAs/InGaP laser heterostructures on a modified Epiquip VP-50-RP installation was developed. Mesa stripe laser diodes with threshold current density J _th=100–200 A/cm², internal optical loss α_i=1.3–1.7 cm^?1, and internal quantum efficiency η_i=60–70% have been fabricated. A CW output optical power of 5 W has been obtained for a single 100-µm-wide aperture mesa stripe laser diode emitting at 1.03 µm. It is shown that use of AlGaAs waveguide layers, which increase the conduction band barrier offset, lowers the temperature sensitivity of laser heterostructures within the temperature range 10–80°C.     

Comparative investigation of InGaP/GaAs pseudomorphic field-effect transistors with triple doped-channel profiles

In this article, the comparison of DC performance on InGaP/GaAs pseudomorphic field-effect transistors with tripe doped-channel profiles is demonstrated. As compared to the uniform and high-medium-low doped-channel devices, the low-medium-high doped-channel device exhibits the broadest gate voltage swing and the best device linearity because more twodimensional electron gases are formed in the heaviest doped channel to enhance the magnitude of negative threshold voltage. Experimentally, the transconductance within 50% of its maximum value for gate voltage swing is 4.62 V in the low-medium-high doped-channel device, which is greater than 3.58 (3.30) V in the uniform (high-medium-low) doped-channel device.     

Simulated analysis for InGaP/GaAs heterostructure-emitter bipolar transistor with InGaAs/GaAs superlattice-base structure

A novel InGaP/GaAs heterostructure-emitter bipolar transistor (HEBT) with InGaAs/GaAs superlattice-base structure is proposed and demonstrated by two-dimensional analysis. As compared with the traditional HEBT, the studied superlattice-base device exhibits a higher collector current, a higher current gain of 246, and a lower base–emitter (B–E) turn-on voltage of 0.966 V at a current level of 1 μA, attributed to the increased charge storage of minority carriers in the InGaAs/GaAs superlattice-base region by tunneling behavior. The low turn-on voltage can reduce the operating voltage and collector–emitter offset voltage for low power consumption in circuit applications.     

1.3 μm InGaAs/GaAs strained quantum well lasers with InGaPcladding layer

Using MOVPE, we fabricated strained quantum well 1.3 μm lasers with an InGaP cladding layer on a GaAs substrate. The lasers had a high gain coefficient of 60 cm^-1. Lasers with high reflection facets had a low threshold current density of 500 A/cm², and a high characteristic temperature of 100 K     

Strained-layer multiple-quantum-well InGaAs/GaAs waveguidemodulators operating around 1 μm

Detailed experimental results on the properties of multiple-quantum-well waveguide modulators on strained InGaAs/GaAs layers are presented. Transmission and photocurrent measurements are performed using a tunable Ti-sapphire-laser. The spectra reveal an absorption edge shift as large as 60 nm at 5 V reverse bias. Optimum performance is achieved around a wavelength of 1 μm, where an extinction ratio of up to 20 dB is obtained with an absorption loss of less than 2 dB/cm. The overall insertion loss of the modulator approaches a constant value of 6.5 dB at higher wavelengths (λ⩾980 nm) which is shown to be mainly affected by coupling losses     

Performance dependence of InGaP/InGaAs/GaAs pHEMTs on gatemetallization

The performance of InGaP-based pHEMTs as a function of gate metallization is examined for Mo/Au, Ti/Au, and Pt/Au gates. DC and microwave performance of pHEMT's with 0.7-μm gate lengths is evaluated. Transconductance, threshold voltage, f_t, and f_max are found to depend strongly on gate metallization. High-speed performance is achieved, with f_t of 41.3 GHz and f _max of 101 GHz using Mo/Au gates. The difference in performance between devices with different gate metallizations is postulated to be due to a combination of the difference in Schottky barrier heights and different gate-to-channel spacings due to penetration of the gate metal into the InGaP barrier layer     

Integration of n- and p-channel InGaP=InGaAs doped-channel pseudomorphic HFETs

n- and p-channel InGaP/InGaAs doped-channel pseudomorphic HFETs on the identical chip by selectively etching process are first demonstrated. Particularly, the saturation voltage of the n-channel device is relatively small because 2DEG is formed and modulated in the InGaAs strain channel. Experimentally, an extrinsic transconductance of 292 (72) mS/mm and a saturation current density of 335 (-270) mA/mm are obtained for the n-channel (p-channel) device. Furthermore, the integrated devices exhibit broad gate voltage swings for linear and signal amplifier applications.     

Highly strained InGaP/InGaAs p-HEMT using reduced area growth

Highly strained InGaP/In_0.33Ga_0.67As pseudomorphic high electron mobility transistor (p-HEMT) structures were grown on patterned GaAs substrates. Performance of the highly strained p-HEMTs grown on patterned substrates was compared with that of highly strained p-HEMTs and conventional InGaP/In_0.22Ga_0.78 As p-HEMTs grown on nonpatterned substrates. The highly strained p-HEMTs grown on patterned substrates showed substantial improvements in dc (transconductance and drain saturation current) and rf (cutoff frequency: f_T and maximum oscillation frequency: f_max ) performances as compared with those of the p-HEMTs grown on nonpatterned substrates. The results indicate the potential of highly strained p-HEMTs using reduced area growth for high-speed device applications