In0.52Al0.48As/In0.53Ga0.47As MSM photodetectors and HEMT's grown by MOCVD on GaAs substrates

The authors report the first demonstration of In_0.52Al _0.48As/In_0.53Ga_0.47As metal-semiconductor-metal (MSM) photodetectors and high-electron-mobility transistors (HEMTs) grown on GaAs substrates by organometallic chemical vapor deposition. Both photodetectors and transistors showed no degradation in performance compared to devices simultaneously grown on InP substrates. The photodetectors exhibited a responsivity of 0.45 A/W and leakage current of 10 to 50 nA. The HEMTs with a gate length of 1.0 μm showed a transconductance as high as 250 mS/mm, and f_T and f_max of 25 and 70 GHz, respectively     

Design and experimental characteristics of strained In0.52Al0.48As/InxGa1-xAs (x>0.53)HEMTs

Strained In_0.52Al_0.48 As/In_xGa _1-xAs (x>0.53) HEMTs (high electron mobility transistors) are studied theoretically and experimentally. A device design procedure is reported that is based on band structure and charge control self-consistent calculations. It predicts the sheet carrier density and electron confinement as a function of doping and thickness of layers. The DC performance at 300 K is presented. Wafer statistics demonstrate improvement of device characteristics with excess indium in the channel (g¯_{m, intr}=500 and 700 mS/mm for x=0.60 and 0.65). Microwave characterization shows the f_T improvement (f_T=40 and 45 GHz for x=0.60 and 0.65, respectively) and the R_ds limitations of the 1-μm-long-gate HEMTs     

Doubly strainedIn0.41Al0.59As/n+-In0.65Ga0.35As HFET with high breakdown voltage

An In_0.41Al_0.59As/n⁺-In_0.65 Ga_0.35As HFET on InP was designed and fabricated, using the following methodology to enhance device breakdown: a quantum-well channel to introduce electron quantization and increase the effective channel bandgap, a strained In_0.41Al_0.59As insulator, and the elimination of parasitic mesa-sidewall gate leakage. The In_0.65Ga_0.35As channel is optimally doped to N_D=6×10¹⁸ cm^-3. The resulting device (L_g=1.9 μm, W_g =200 μm) has f_t=14.9 GHz, f_max in the range of 85 to 101 GHz, MSG=17.6 dB at 12 GHz V_B=12.8 V, and I_D(max)=302 mA/mm. This structure offers the promise of high-voltage applications at high frequencies on InP     

0.2-μm gate-length atomic-planar doped pseudomorphic Al0.3Ga0.7As/In0.25Ga0.75As MODFETswith fT over 120 GHz

The authors report the DC and RF performance of nominally 0.2-μm-gate length atomic-planar doped pseudomorphic Al_0.3Ga_0.7As/In_0.25Ga_0.75As modulation-doped field-effect transistors (MODFETs) with f_T over 120 GHz. The devices exhibit a maximum two-dimensional electron gas (2 DEG) sheet density of 2.4×10¹² cm^-2, peak transconductance g _m of 530-570 mS/mm. maximum current density of 500-550 mA/mm, and peak current-gain cutoff frequency f_T of 110-122 GHz. These results are claimed to be among the best ever reported for pseudomorphic AlGaAs/InGaAs MODFETs and are attributed to the high 2 DEG sheet density, rather than an enhanced saturation velocity, in the In_0.25Ga_0.75As channel     

Gate-length dependence of DC and microwave properties ofsubmicrometer In0.53Ga0.47As HIGFETs

In_0.52Al_0.48As/In_0.53Ga_0.47 As/InP heterostructure insulated-gate field-effect transistors (HIGFETs) with gate lengths from 1.1 and 0.3 μm have been fabricated, and their electrical performance is characterized at DC and microwave frequencies. The refractory-gate self-aligned process, applied to devices with In_0.53Ga_0.47As channels, yields an unprecedented combination of very-high speed and excellent uniformity. HIGFETs with L_g=0.6 μm showed average peak transconductance g_m of 528 mS/mm and unity-current-gain cutoff frequency f_t of 50 GHz. The uniformity of g_m was better than 1%, and the voltage of the g_m peak was uniform to ±30 mV. HIGFETs with L_g=0.3 μm showed f₁ up to 63 GHz, but suffered from serious short-channel effect, due to excessive thickness of the InGaAs channel layer. A self-aligned technique for gate resistance reduction is shown to substantially improve microwave power gain     

Characterization of surface-undoped In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobilitytransistors

High-performance 0.3-μm-gate-length surface-undoped In_0.52 Al_0.48As/In_0.53Ga_0.47As/InP high-electron-mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) have been characterized and compared with a surface-doped structure. At 18 GHz, the surface-undoped HEMT has achieved a maximum stable gain (MSG) of 19.2 dB compared to 16.0 dB for the surface-doped structure. The higher MSG value of the surface-undoped HEMTs is obtained due to the improved g_m/g₀ ratio associated with the surface-induced electric field spreading effect. Comparison of identical 0.3-×150-μm-gate devices fabricated on surface-undoped and -doped structures has shown greatly improved gate leakage characteristics and much lower output conductance for the surface-undoped structure. It is demonstrated that the surface potential, modulated by different surface layer designs, affects the charge control in the conducting channel, especially the carrier injection into the buffer, resulting in excess output conductance. Several millimeter-wave coplanar waveguide (CPW) monolithic distributed amplifiers have been successfully fabricated by using the surface-undoped HEMT structure. A high gain per stage distributed amplifier with 170-dB±1-dB small-signal gain across a frequency band of 24-40 GHz, a W-band monolithic integrated circuit with 6.4-dB gain at 94 GHz, and a broad bandwidth distributed amplifier with 5-dB gain across a frequency band of 5 to 100 GHz have been demonstrated by using the surface-undoped structures     

Unstrained, modulation-doped, In0.3Ga0.7As/In0.29Al0.71As field-effect transistor grown on GaAssubstrate

The fabrication, structure, and properties of unstrained modulation-doped, 1-μm-long and 10-μm-wide gate, field effect transistors made of In_0.3Ga_0.7As/In_0.29As_0.71As heterojunctions grown on GaAs substrates using compositionally step-graded buffer layers are described. These devices have a transconductance of 335 mS/mm, f_max of 56 GHz, and a gate breakdown voltage of 23.5 V     

In0.52Al0.48As/InxGa1-xAs (0.53⩽x⩽0.70) lattice-matched and strainedheterostructure insulated-gate FETs

The DC and microwave properties of In_0.52Al_0.48 Al/In_xGa_1-xAs (0.53⩽x⩽0.70) heterostructure insulated gate field-effect transistors (HIGFETs) with a quantum well channel design are presented. DC and microwave transconductances (g_m) are enhanced as the In content is increased in the InGaAs channel. An intrinsic microwave g _m value of 428 mS/mm and a K-factor of 1140 mS/mm-V have been obtained for 1.0-μm gate length with the 65% In channel devices. The sheet charge density, drift mobility, transconductance, current-gain cutoff frequency (f_T), and maximum oscillation frequency (f _max) all show a continuous improvement up to 65% In content ( f_T=22.5 GHz with 53% and f_T=27 GHz with 65% In; the corresponding f_max change is from 6.5 to 8 GHz). The device performance degrades as the In content is increased to 70%. DC and microwave characteristics show the presence of negative differential resistance (NDR) up to 2.7 GHz     

Bias dependence of fT and fmax in anIn0.52Al0.48As/n+-In0.53Ga0.47As MISFET

Detailed microwave characterization of a recently fabricated In _0.52Al_0.48As/n⁺-In_0.53Ga _0.47As MISFET reveals that high values of current-gain cutoff frequency (f_T) and unilateral-gain cutoff frequency (f_max) are obtained for a broad range of gate bias voltage values. A significant peak in f_T and f _max has also been observed at high gate-source bias values. The peak coincides with the onset of electron accumulation at the heterointerface and is attributed to reduced ionized impurity scattering coupled with reduced drain conductance. This result suggests an improved device structure that optimizes operation in the accumulation regime     

W-band low-noise InAlAs/InGaAs lattice-matched HEMTs

Very low-noise 0.15-μm gate-length W-band In_0.52 Al_0.48As/In_0.53Ga_0.47As/In _0.52Al_0.48As/InP lattice-matched HEMTs are discussed. A maximum extrinsic transconductance of 1300 mS/mm has been measured for the device. At 18 GHz, a noise figure of 0.3 dB with an associated gain of 17.2 dB was measured. The device also exhibited a minimum noise figure of 1.4 dB with 6.6-dB associated gain at 93 GHz. A maximum available gain of 12.6 dB at 95 GHz, corresponding to a maximum frequency of oscillation, f_max, of 405 GHz (-6-dB/octave extrapolation) in the device was measured. These are the best device results yet reported. These results clearly demonstrate the potential of the InP-based HEMTs for low-noise applications, at least up to 100 GHz     

Low-temperature microwave characteristics of pseudomorphic InxGa1-xAs/In0.52Al0.48Asmodulation-doped field-effect transistors

Low-temperature microwave measurements of both lattice-matched and pseudomorphic In_xGa_1-xAs/In_0.48As (x=0.53, 0.60, and 0.70) channel MODFETs on InP substrates were carried out in a cryogenic measurement system. The measurements were done in the temperature range of 77 to 300 K and in the frequency range of 0.5 to 11.0 GHz at different bias conditions. The cutoff frequency ( f_T) for the In_xGa_1-xAs/In_0.52Al_0.48As MODFETs improved from 22 to 29 GHz, 29 to 38 GHz, and 39 to 51 GHz, for x=0.53, 0.60, and 0.70, respectively, as the temperature was lowered from 300 to 77 K, which is approximately a 31% increase at each composition. No degradations were observed in device performance. These results indicate an excellent potential of the pseudomorphic devices at low temperatures     

Electron transport in 0.15-μm gate In0.52Al0.48As/In0.53Ga0.47As HEMT

Magneto-transport and cyclotron resonance measurements were made to determine directly the density, mobility, and the effective mass of the charge carriers in a high-performance 0.15-μm gate In_0.52 Al_0.48As/In_0.53Ga_0.47As high-electron-mobility transistor (HEMT) at low temperatures. At the gate voltage V_G=0 V, the carrier density n _g under the gate is 9×10¹¹ cm^-2, while outside of the gate region n_g=2.1×10¹² cm^-2. The mobility under the gate at 4.2 K is as low as 400 cm²/V-s when V_G<0.1 V and rapidly approaches 11000 cm²/V-s when V_G>0.1 V. The existence of this high mobility threshold is crucial to the operation of the device and sets its high-performance region in V_G>0.1 V     

Millimeter-wave ion-implanted gradedInxGa1-xAs MESFETs grown by MOCVD

The authors present the fabrication and characterization of ion-implanted graded In_xGa_1-xAs/GaAs MESFETs. The In_xGa_1-xAs layers are grown on GaAs substrates by MOCVD (metal-organic chemical vapor deposition) with InAs concentration graded from 15% at the substrate to 0% at the surface. 0.5-μm gate MESFETs are fabricated on these wafers using silicon ion implantation. In addition to improved Schottky contact, the graded In_xGa _1-xAs MESFET achieves maximum extrinsic transconductance of 460 mS/mm and a current-gain cutoff frequency f_t of 61 GHz, which is the highest ever reported for a 0.5-μm gate MESFET. In comparison, In_0.1Ga_0.9As MESFETs fabricated with the same processing technique show an f_t of 55 GHz     

Highly lattice-mismatched In0.26Ga0.74As/GaAsMESFET's: impact of critical thickness on device performance

Fabrication of 0.25-μm-gate MESFETs directly on In_0.26 Ga_0.74As epitaxial layers which are much thicker than the pseudomorphic critical thickness is described. The InAs mole fraction is increased in the MESFET channel to 26%. Whether the device performance can be further improved without detrimental dislocation effects as the channel thickness exceeds the critical thickness considerably is investigated. Despite large lattice mismatch and high defect density, these devices show excellent microwave performance with an extrinsic f_t of 120 GHz. Bias-dependent S-parameters indicate that the In_0.26Ga_0.74As MESFET maintains excellent device performance down to very low drain current without showing any performance degradation due to misfit or threading dislocations     

Metamorphic In0.4Al0.6As/In0.4Ga0.6As HEMTs on GaAs substrate

New In_0.4Al_0.6As/In_0.4Ga_0.6 As metamorphic (MM) high electron mobility transistors (HEMTs) have been successfully fabricated on GaAs substrate with T-shaped gate lengths varying from 0.1 to 0.25 μm. The Schottky characteristics are a forward turn-on voltage of 0.7 V and a gate breakdown voltage of -10.5 V. These new MM-HEMTs exhibit typical drain currents of 600 mA/mm and extrinsic transconductance superior to 720 mS/mm. An extrinsic current cutoff frequency f_T of 195 GHz is achieved with the 0.1-μm gate length device. These results are the first reported for In_0.4 Al_0.6As/In_0.4Ga_0.6As MM-HEMTs on GaAs substrate     

Single and dual p-doped channel In0.52Al0.48As/InxGa1-xAs (x=0.53, 0.65) FET's andthe role of doping

The properties of lattice-matched (x=0.53) and strained ( x=0.65) In_0.52Al_0.48As/In_xGa _1-xAs p-doped channel FETs are reported. The role of doping density is studied with the help of two designs (dual-channel with low doping and single-channel with high doping). The strained dual-channel devices demonstrated an improvement of mobility from 108 cm²/V-s (53% In) to 265 cm²/V-s (65% In) at 300 K. The corresponding intrinsic transconductance enhancement is from 23 Ms/mm (53% In) to 46.5 mS/mm (65% In) using 1.0 μm-long gates. The cutoff frequency (f_t) also improves from 1.0 to 1.4 GHz. The impact of strain in the highly-doped single-channel device is small. The band structure under lattice-matched and strained conditions and the position of the Fermi level according to doping seem to be the main factors determining the reported features     

The influence of gate-feeder/mesa-edge contacting on sidegatingeffects in In0.52Al0.48As/In0.53Ga0.47As heterostructure FET's

Sidegating effects in InAlAs/InGaAs heterostructure field effect transistors (HFETs) were experimentally investigated. Two different configurations of gate feeder across the mesa edges are compared in In _0.52Al_0.48As/In_0.53Ga_0.47As. HFETs. HEMTs and heterostructure insulated-gate FETs (HIGFETs) were fabricated, each with different gate-feeder configurations. HFETs with the gate air bridge over the mesa edge can maintain 99% of the drain-source (I_ds) current level at sidegate voltages (V_sg) extending up to -30 V, while the non-air-bridge configuration of HFETs show a 30% drop of I_ds at the same V _sg. This significant discrepancy of sidegating effect is attributed to depletion region modulation at the mesa edge below the gate feeder. By lifting the gate feeder above the mesa step, sidegating is reduced, which suggests the channel/substrate trap effects are negligibly small. The role of air-bridge structures in determining the sidegating characteristics is discussed     

High-performance highly strainedGa0.23In0.77As/Al0.48In0.52As MODFET's obtained by selective and shallow etch guide recesstechniques

Record high f_TL_g products of 57 and 46 GHz-μm have been achieved in Ga_1-x In_x As/AlInAs MODFETs with a strain compensated channel of x=0.77 and a lattice-matched channel of x=0.53, respectively. Although g_m as high as 950 mS/mm has been obtained by conventional deep recess for the gate, these latter devices show a prominent kink effect which lowers f_T and the voltage gain. By limiting the depth of final nonselective recess etch to 3 nm with the help of selective step etches, f_T as high as 47 GHz and g_m as high as 843 mS/mm have been achieved for MODFETs with x=0.77 and L_g=1.1 μm     

Low-frequency noise characteristics of lattice-matched(x=0.53) and strained (x>0.53) In0.52Al0.48As/InxGa1-xAs HEMT's

Extensive bias-dependent and temperature-dependent low-frequency (LF) noise measurements were performed on lattice-matched and strained In_0.52Al_0.48As/In_xGa_1-x As(0.53<x<0.70) HEMTs. The input-noise voltage spectra density is insensitive to V_DS bias and shows a minimum at V_GS corresponding to the peak g_m condition. The corresponding output-noise voltage spectral density, which depends strongly on the gain of the devices, increases with V_DS. The input noise was rather insensitive to indium (In) content. Temperature-dependent low-frequency noise measurements on these devices reveal shallow traps with energies of 0.11, 0.15, and 0.18 eV for 60%, 65%, and 70% In HEMTs. Noise transition frequencies for these devices were on the order of 200-300 MHz and remain almost the same for different channel In content and V_DS bias     

Effect of hot-electron injection of high-frequency characteristicsof abrupt In0.52(Ga1-xAlx)0.48As/InGaAs HBT's

The effect of hot-electron injection energy (E_i) into the base on the high-frequency characteristics of In_0/52(Ga_1-xAl_x)_0.48 As/InGaAs abrupt heterojunction bipolar transistors (HBTs) is investigated by changing the composition of the emitter. There exists an optimum E_i at which a maximum current gain cutoff frequency (ft) is obtained. Analysis of hot-electron transport in the base and collector by Monte Carlo simulation is carried out to understand the above phenomenon. The collector transit time (τ_c ) increases with E_i, because electrons with higher energy transfer from the Γ valley into the upper L and X valleys. At first, the base transit time (τ_b ) decreases with E_i at the low E_i region. However, τ_b does not decrease monotically with E_i, because of the nonparabolicity in the energy-band structure of InGaAs. Consequently, there exists a minimum in the sum of τ_b and τ_c , in other words a maximum f_t, at an intermediate value of E_i