High-field transport in InGaAs/InAlAs modulation-doped heterostructures

The velocity-field and mobility-field characteristics of normal and inverted InGaAs/InAlAs modulation-doped heterostructures grown by molecular-beam epitaxy have been measured at 300 and 77 K. Veloczities of 3.0 × 10⁷and 1.7 × 10⁷cm/s have been measured in the normal and inverted structures, respectively, at 77 K. Current instabilities are observed at the corresponding field values. Hall mobilities decrease With field beyond 500 V/cm, principally due to phonon scattering. The mobilities in normal and inverted heterostructures attain Similar values at fields higher than 1 kV/cm, irrespective of the low-field values.     

Metamorphic InAlAs/InGaAs enhancement mode HEMTs on GaAs substrates

In_0.5Al_0.5As/In_0.5Ga_0.5 As HEMTs have been grown metamorphically on GaAs substrates oriented 6° off (100) toward (111)A using a graded InAlAs buffer. The devices are enhancement mode and show good dc and RF performance. The 0.6-μm gate length devices have saturation currents of 262 mA/mm at a gate bias of 0.7 V and a peak transconductance of 647 mS/mm. The 0.6 μm×3 mm devices tested on-wafer have output powers up to 30 mW/mm and 46% power-added-efficiency (PAE) at 1 V drain bias and 850 MHz. When biased and matched for best efficiency performance, this same device has up to 68% PAE at V_d=1 V     

Electron mobility and drift velocity in selectively doped InAlAs/InGaAs/InAlAs heterostructures

An increase in the electron mobility and drift velocity in high electric fields in quantum wells of selectively doped InAlAs/InGaAs/InAsAs heterostructures is obtained experimentally via controlling the composition of semiconductors forming the interface. The electron mobility at the interface in the In_0.8Ga_0.2As/In_0.7Al_0.3As metamorphic structure with a high molar fraction of In (0.7–0.8) is as high as 12.3 × 10³ cm² V⁻¹ s⁻¹ at room temperature. An increase in the electron mobility by a factor of 1.1–1.4 is attained upon the introduction of thin (1–3 nm) InAs layers into a quantum well of selectively doped In_0.53Ga_0.47As/In_0.52Al_0.48As heterostructures. A maximal drift velocity attains 2.5 × 10⁷ cm/s in electric fields of 2–5 kV/cm. The threshold field F _th for the intervalley Γ-L electron transfer (the Gunn effect) in the InGaAs quantum well is higher than in the bulk material by a factor of 2.5–3. The effect of two- to threefold decrease in the threshold field F _th in the InGaAs quantum well is established upon increasing the molar fraction of In in the InAlAs barrier, as well as upon the introduction of thin InAs inserts into the InGaAs quantum well.     

Metamorphic InAlAs/InGaAs HEMTs on GaAs substrates with a novelcomposite channels design

We report on fabrication and performance of novel 0.13 μm T-gate metamorphic InAlAs/InGaAs HEMTs on GaAs substrates with composite InGaAs channels, combining the superior transport properties of In_0.52Ga_0.48As with low-impact ionization in the In_0.32Ga_0.68As subchannel. These devices exhibit excellent DC characteristics, high drain currents of 750 mA/mm, extrinsic transconductances of 600 mS/mm, combined with still very low output conductance values of 20 mS/mm, and high channel and gate breakdown voltages. The use of a composite InGaAs channels leads to excellent cut-off frequencies: f_max of 350 GHz and an f_T 160 GHz at V_DS=1.5 V. These are the best microwave frequency results ever reported for any FET on GaAs substrate     

Characteristics of InAlAs/InGaAs high electron mobility transistorsunder 1.3-μm laser illumination

The current-voltage (I-V) characteristics of InAlAs/InGaAs high electron mobility transistors (HEMTs) under illumination are investigated. The change of the drain current caused by the illumination can be explained by using the photovoltaic effect so that the excess holes photo-generated in the InGaAs channel layer accumulate at the source-electrode region and cause an effective decrease in the potential barrier for electrons between the source and the channel. The basic equations describing this phenomenon are derived on the basis of the experimental results. In addition, our experimental results are shown to support the barrier-induced hole pile-up model in which holes generated by the impact ionization accumulate in the InAlAs barrier on the source side and cause the kink effect In InAlAs/InGaAs HEMTs     

MOCVD-grown AlGaN/GaN heterostructures with high electron mobility

Specific features of MOCVD growth of AlGaN/GaN heterostructures have been studied. In the structures obtained, the 2D electron gas in the channel had a density of 1.2×10¹³ cm^?2 and a mobility of 1290 cm²/(V s) at room temperature. The effect of the purity of starting components on the properties of the structure is studied.     

MOVPE grown InAlAs/InGaAs/InP MODFETs with very high f/sub T/

High-performance 0.15 mu m gate length modulation-doped field-effect transistors (MODFETs) have been fabricated on a lattice-matched InAlAs/InGaAs heterostructure grown by organic vapour phase epitaxy (MOVPE). Excellent 'kink-free' DC characteristics with extrinsic transconductance g/sub m/ of 1080 mS/mm at a drain current of 508 mA/mm have been achieved. A unity current-gain cutoff frequency f/sub T/ of 187 GHz at room temperature has been measured, which is the highest value reported for MOVPE-grown lattice-matched InAlAs/InGaAs MODFETs.<>     

Structural characterization of InGaAs/InAlAs quantum wells grown on 0 (111)-InP substrates

Recent studies on HEMT structures according to their growth orientation have attracted much interest from the viewpoint of physics and novel device applications. However, the optimization of their properties needs a high degree of crystalline quality. In this work, the structural characteristics of the layers present on InGaAs/InAlAs HEMT structures grown on (111)-InP substrates have been analyzed by atomic force and transmission electron microscopies. The presence of a strained quantum well induces a defect structure and surface morphology quite different from those observed in similar samples without the quamtum well. These results show that an accurate control of the growth conditions is necessary to obtain acceptable structural quality for (111) devices.     

Maximum drift velocity of electrons in selectively doped InAlAs/InGaAs/InAlAs heterostructures with InAs inserts

The dependence of the electron mobility and drift velocity on the growth conditions, thickness, and doping of an InAs insert placed at the center of the quantum well in a selectively doped InAlAs/InGaAs/InAlAs heterostructure has been investigated. Record enhancement of the maximum drift velocity to (2–4) × 10⁷ cm/s in an electric field of 5 × 10³ V/cm has been obtained in a 17-nm-wide quantum well with an undoped 4-nm-thick InAs insert. In the structures with additional doping of the InAs insert, which facilitates an increase in the density of electrons in the quantum well to 4.0 × 10¹² cm^?2, the maximum drift velocity is as high as 2 × 10⁷ cm/s in an electric field of 7 × 10³ V/cm.     

Charge storage in InAlAs/InGaAs/InP floating gate heterostructures

Charge retention in floating gate InAlAs/InGaAs/InP field effect transistors is limited by lateral electron motion along the storage channel, a different direction for motion than found for AlAs/GaAs devices. Storage times as a function of temperature for the InP based alloy devices are reported and compared with similar AlAs/GaAs devices by using Poisson equation models.<>     

High-performance, 0.1 μm InAlAs/InGaAs high electron mobilitytransistors on GaAs

This letter describes the material characterization and device test of InAlAs/InGaAs high electron mobility transistors (HEMTs) grown on GaAs substrates with indium compositions and performance comparable to InP-based devices. This technology demonstrates the potential for lowered production cost of very high performance devices. The transistors were fabricated from material with room temperature channel electron mobilities and carrier concentrations of μ=10000 cm² /Vs, n=3.2×10¹² cm^-2 (In=53%) and μ=11800 cm²/Vs, n=2.8×10¹² cm^-2 (In=60%). A series of In=53%, 0.1×100 μm² and 0.1×50 μm² devices demonstrated extrinsic transconductance values greater than 1 S/mm with the best device reaching 1.074 S/mm. High-frequency testing of 0.1×50 μm² discrete HEMT's up to 40 GHz and fitting of a small signal equivalent circuit yielded an intrinsic transconductance (g_m,i) of 1.67 S/mm, with unity current gain frequency (f_T) of 150 GHz and a maximum frequency of oscillation (f_max) of 330 GHz. Transistors with In=60% exhibited an extrinsic g_m of 1.7 S/mm, which is the highest reported value for a GaAs based device     

InGaAs/InAlAs SCH-MQW lasers with superlattice optical confinementlayers grown by MBE

InGaAs/InAlAs separate-confinement-heterostructure multiple-quantum-well (SCH-MQW) lasers with superlattice optical confinement layers grown by molecular beam epitaxy are discussed. Room-temperature operation with a low threshold current density of 1.7 kA/cm² at 1.537 μm wavelength is obtained for these lasers     

Scattering and electron mobility in combination-doped HFET-structures AlGaAs/InGaAs/AlGaAs with high electron density

Molecular-beam epitaxy is used for growing structures differing in doping technique and doping level and having a high two-dimensional-electron concentration n _s in the quantum well. The effect of doping combining uniform and δ doping on the electron-transport properties of heterostructures is investigated. A new type of structure with a two-sided silicon δ doping of GaAs transition layers located on the quantum-well boundaries is proposed. The largest value of electron mobility μ_H = 1520 cm²/(V s) is obtained simultaneously with a high electron density n _s = 1.37 × 10¹³ cm⁻² at 300 K with such a doping. It is associated with decreasing electron scattering by an ionized impurity, which is confirmed by the carried out calculations.     

Selective photochemical dry etching of GaAs/AlGaAs and InGaAs/InAlAs heterostructures

Selective photochemical dry etching of GaAs layers on AlGaAs using HCl gas and InGaAs layers on InAlAs using CH/sub 3/Br gas is studied. A low pressure mercury lamp was used as the deep UV light source. A selectivity of more than 150 for GaAs over AlGaAs and more than 60 for InGaAs over InAlAs was obtained.<>     

Extremely low noise InGaAs/InAlAs HEMT grown by MOCVD

MOCVD-grown InGaAs/InAlAs HEMTs with excellent noise performance comparable to that of MBE-grown devices have been successfully fabricated. A minimum noise figure lower than 0.30 dB has been obtained with an associated gain of approximately 15 dB at 12 GHz. Furthermore, devices in ceramic packages have exhibited a minimum noise figure of 0.42 dB.<>     

Detection of lead ions with AlGaAs/InGaAs pseudomorphic high electron mobility transistor

Lead poisoning is a serious environmental concern, which is a health threat. Existing technologies always have some drawbacks, which restrict their application ranges, such as real time monitoring. To solve this problem, glutathione was functionalized on the Au-coated gate area of the pseudomorphic high electron mobility transistor (pHEMT) to detect trace amounts of Pb²⁺. The positive charge of lead ions will cause a positive potential on the Au gate of the pHEMT sensor, which will increase the current between the source and the drain. The response range for Pb²⁺ detection has been determined in the concentrations from 0.1 pmol/L to 10 pmol/L. To our knowledge, this is currently the best result for detecting lead ions.     

MOVPE InGaAs/InP grown directly on GaAs substrates

We have demonstrated the feasibility of growth of InP/InGaAs structures directly on GaAs using atmospheric pressure metal organic vapour phase epitaxy. Growth conditions and the equipment used are described along with some preliminary measurements on the GaAs/InP/InGaAs wafers. P-N junctions were formed in these materials to evaluate diode characteristics.     

Very high gain millimeter-wave InAlAs/InGaAs/GaAs metamorphicHEMT's

We report the first demonstration of W-band metamorphic HEMTs/LNA MMICs using an AlGaAsSb lattice strain relief buffer layer on a GaAs substrate. 0.1×50 μm low-noise devices have shown typical extrinsic transconductance of 850 mS/mm with high maximum drain current of 700 mA/mm and gate-drain breakdown voltage of 4.5 V. Small-signal S-parameter measurements performed on the 0.1-μm devices exhibited an excellent f_T of 225 GHz and maximum stable gain (MSG) of 12.9 dB at 60 GHz and 10.4 dB at 110 GHz. The three-stage W-band LNA MMIC exhibits 4.2 dB noise figure with 18 dB gain at 82 GHz and 4.8 dB noise figure with 14 dB gain at 89 GHz, The gain and noise performance of the metamorphic HEMT technology is very close to that of the InP-based HEMT     

Electron properties of surface InGaAs/InAlAs quantum wells with inverted doping on InP substrates

The electron-transport and optical properties of heterostructures with a surface InGaAs/InAlAs quantum well in the cases of inverted δ doping with Si atoms (below the quantum well) and of standard δ doping (above the quantum well) are compared. It is shown that, in the case of inverted doping, the two-dimensional electron density in the quantum well is increased in comparison with the case of the standard arrangement of the doping layer at identical compositions and thicknesses of other heterostructure layers. The experimentally observed features of low-temperature electron transport (Shubnikov–de Haas oscillations, Hall effect) and the photoluminescence spectra of heterostructures are interpreted by simulating the band structure.     

Electrochemically induced asymmetrical etching in InAlAs/InGaAs heterostructures for MODFET gate-groove fabrication

We have achieved a self-controlled asymmetrical etching in metalorganic chemical vapor deposition-grown InAlAs/InGaAs heterostructures, which can be suitable for fabricating modulation-doped field-effect transistors (MODFETs) with gate-groove profiles for improved performance. The technology is based on electrochemical etching phenomena, which can be effectively controlled by using different surface metals for ohmic electrodes. When surface metals of Pt and Ni are deposited on the source and the drain, respectively, the higher electrode potential of Pt results in slower etching on the source side than on the drain side. Thus, asymmetry of gate grooves can be formed by wet-chemical etching with citric-acid-based etchant. This represents a new possibility to conduct “recess engineering” for InAlAs/InGaAs MODFETs.