Strained layer InxGa1-xAs/GaAs and InxGa1-xAs/InyGa1-yPmultiple-quantum-well optical modulators grown by gas-source MBE

The first results on low-power p-i-n diode modulator structures using strained multiple quantum wells (MQW's) of InGaAs/InGaP grown by gas-source molecular beam epitaxy (MBE) on GaAs are presented. A comparison of transmission, reflection, and photocurrent spectra for these nonresonant devices with those fabricated from InGaAs/GaAs indicates larger modulation, with a maximum change in reflection of >42% observed at 5-V bias at a wavelength of 0.96 μm     

High-performance InGaP/InxGa1-xAs HEMT withan inverted delta-doped V-shaped channel structure

This letter reports a new and high-performance InGaP/In_xGa_1-xAs high electron mobility transistor (HEMT) with an inverted delta-doped V-shaped channel. Due to the presence of V-shaped inverted delta-doped InGaP/In_xGa_1-x As structure, good carrier confinement and a flat and wide transconductance operation regime are expected. Experimentally, the fabricated device (1×100 μm²) shows a high gate-to-drain breakdown voltage of 30 V and a high output drain saturation current density of 826 mA/mm at V_GS=2.5 V. The high transconductance expands over a very broad operation range with the maximum value of 201 mS/mm at 300 K. Meanwhile, the studied device exhibits a good microwave frequency linearity     

An anisotype GaAs/InxGa1-xAs heterojunctionfield-effect transistor for digital logic applications

An anisotype heterojunction field-effect transistor (A-HJFET) for GaAs digital integrated circuit applications is proposed. A thin, highly doped, strained In_xGa_1-xAs (x⩽0.2) n-channel is employed for improved transconductance while a p⁺-GaAs cap is used to enhance the dynamic gate voltage range of the device. Prototype devices with 5-μm gate lengths show a maximum transconductance of 80 mS/mm at V_ds=2 V and a forward gate bias voltage of up to +2 V without significant leakage current     

A high-performance δ-dopedGaAs/InxGa1-xAs pseudomorphic high electronmobility transistor utilizing a graded InxGa1-xAschannel

A δ-doped GaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (HEMT) utilizing a graded In composition InGaAs channel grown by low-pressure metalorganic chemical vapor deposition was demonstrated. This structure had an extrinsic transconductance as high as 175 (245) mS/mm and a saturation current density a high as 500 (690) mA/mm at 300 (77) K for a gate length of 2 μm. The maximum transconductance versus gate bias extended over a broad and flat region of more than 2 V at 300 K. A low gate leakage current (<10 μA at -7 V) at 300 K was obtained     

60-GHz noise performance of ion-implanted InxGa1-xAs MESFET's

The authors report the 60-GHz noise performance of low-noise ion-implanted In_xGa_1-xAs MESFETs with 0.25 μm T-shaped gates and amplifiers using these devices. The device noise figure was 2.8 dB with an associated gain of 5.6 dB at 60 GHz. A hybrid two-state amplifier using these ion-implanted In_xGa_1-x As MESFETs achieved a noise figure of 4.6 dB with an associated gain of 10.1 dB at 60 GHz. When this amplifier was biased at 100% I _dss, it achieved 11.5-dB gain at 60 GHz. These results, achieved using low-cost ion-implantation techniques, are the best reported noise figures for ion-implanted MESFETs     

Mobility of strained and dislocatedInxGa1-xAs semiconductor material

A theoretical investigation of low-field electron transport properties in thick layers of partially strain-relieved lattice-mismatched In_xGa_1-xAs on GaAs semiconductor material is performed. The results indicate that room-temperature improvements in low-field mobility with increasing indium concentration are possible, but only occur if the density of misfit dislocations can be held below a critical value     

On the improvement of gate voltage swings in δ-doped GaAs/InxGa1-xAs/GaAs pseudomorphic heterostructures

Significant improvements in gate voltage swings in heterostructures prepared by low-pressure metalorganic chemical vapor deposition are discussed. Structures utilizing a compositionally graded In_xGa_1-xAs channel exhibited a very flat transconductance region of 2 V. The gate voltage swings of single and double δ-doped GaAs/In_0.25Ga_0.75As/GaAs structures were 2.5 and 2.8 V, respectively. All structures also exhibited high extrinsic transconductance as well as high saturation current densities     

Short pulse transfer characteristics of AlxGa1-xAs/GaAs andAlxGa1-xAs/InyGa1-yAsmodulation-doped heterojunction FET's

Short-pulse drain current versus gate voltage transfer characteristics measured for modulation-doped HFETs (MODFETs) with four donor-layer-channel-layer combinations-(1) Al_0.3Ga_0.7 As-GaAs, (2) Al_0.2Ga_0.8As-GaAs, (3) Al_0.3Ga_0.7As-In_0.2Ga_0.8As, and (4) Al_0.2Ga_0.8As-In_0.2 a_0.8 As-are compared with the DC transfer characteristics. The measurements are relevant to high-speed switching in HFET circuits. Significant shifts in threshold voltage are observed between the DC and short-pulse characteristics for the structures with n⁺-Al_0.3Ga_0.7As donor layers, while the corresponding shifts for structures with n⁺-Al_0.2Ga_0.8As donor layers are relatively small or virtually nonexistent     

Observation of the multiple negative-differential-resistance ofmetal-insulator-semiconductor-like structure with step-compositioned InxGa1-xAs quantum wells

An interesting multiple negative-differential-resistance (MNDR) device, based on an AlGaAs-InGaAs-GaAs metal-insulator-semiconductor (MIS)-like structure, has been fabricated and demonstrated. Three and six switching phenomena have been observed at room temperature and -105°C, respectively. The impressive MNDR behaviors are believed to be caused by the sequential accumulation process of carriers at In_x Ga_1-xAs subwells and the successive barrier lowering and potential redistribution effects. These effects yield the step by step enhancement of tunneling through the “insulated” AlGaAs barrier. It is known that, from experimental results, the temperature variation plays an important role on carriers transport and experimental current-voltage (I-V) characteristics     

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     

High peak-to-valley current ratioIn0.22Ga0.78As/AlAs RTDs on GaAs using relaxed InxGa1-x buffers

The authors have grown In_0.22Ga_0.78As/AlAs resonant tunnelling diodes (RTDs) on relaxed In_xGa_1-x As buffers on GaAs substrates, which show the largest peak-to-valley current ratio (PVCR), 13:1, ever reported for GaAs-based RTDs. X-ray diffraction and photoluminescence (PL) studies confirm the composition and relaxation of the buffers. The intrinsic device performance is excellent despite the presence of some dislocations in the active layers. However, it appears that the relaxed buffers do add series resistance to the intrinsic device     

Wide-band transimpedance amplifiers using AlGaAs/InxGa1-xAs pseudomorphic 2-DEG FET's

Monolithic wide-band amplifiers have been demonstrated using AlGaAs/In_xGa_1-xAs/GaAs pseudomorphic two-dimensional electron-gas field-effect transistors. The amplifiers have yielded an 18.0 GHz bandwidth and a 41.8 dBΩ transimpedance gain with a feedback resistance of 100 Ω. In addition, the dependence of In mole fraction for an In_xGa_1-xAs channel layer on device and amplifier performance has been also investigated. The g_m and the f_T in a device, along with the bandwidth, the gain, and the noise performance in an amplifier, have improved as the In mole fraction is varied from 0 to 0.25     

Modeling of short-pulse threshold voltage shifts due to DX centersin AlxGa1-xAs/GaAs and AlxGa1-xAs/InyGa1-yAs MODFET's

The DX-center-related short-pulse threshold voltage shifts (SPTVS) in Al_xGa_1-xAs-based MODFETs is modeled using CBAND, a simulator that solves Poisson equations self-consistently with Schrodinger equations and donor statistics. Using values given in the literature for the DX energy level in Al_xGa_1-xAs this technique gives good agreement between measured and simulated SPTVS for Al_0.3Ga_0.7As/GaAs and Al_0.3Ga_0.7As/In_0.2Ga_0.8As MODFETs. Both simulation and experiment show that the use of Al_0.2 Ga_0.8As in the donor layer reduces the SPTVS relative to the structures using Al_0.3Ga_0.7As. However, the measured shifts at this composition are considerably lower than the simulated values, indicating a DX energy level that may be higher than the value extrapolated from the literature, possibly due to the existence of multiple trap levels. Despite this discrepancy, these results support the use of strained-channel layers and lower Al_x Ga_1-xAs compositions in MODFETs for digital and other large-signal applications requiring good threshold stability     

衬底温度和生长速率对MBE自组织生长InxGa1-xAs/GaAs QD的影响

研究GaAs基In     

Dislocation scattering in n-type modulation dopedAl0.3Ga0.7As/InxGa1-xAs/Al0.3Ga0.7As quantum wells

The mobility due to misfit dislocation scattering in n-type modulation doped Al_0.3Ga_0.7As/In_xGa_1-xAs/Al _0.3Ga_0.7As quantum wells is discussed. Initially, the dislocations are modeled as an array of orthogonal charged lines. The scattering potential is introduced, including both the coulombic and piezoelectric components. The expression for the mobility limited by dislocation scattering is established, and the anisotropic characteristics of mobility and its variation with various material and device parameters are presented and discussed     

High-speed InGaP/GaAs transistors with a sidewall base contactstructure

We have fabricated InGaP/GaAs double heterojunction bipolar transistors with a sidewall base contact structure. These transistors operate in both emitter-up and emitter-down modes. Symmetric characteristics of the cutoff frequency f_T=68 GHz and the maximum oscillation frequency f_max=31 GHz were obtained at a base-collector bias V_BC of 0 V. For emitter-down operation, f _T was found to reach a maximum of 78 GHz when the base-collector junction was forward biased at 0.9 V. The product of f _T for emitter-down operation and f_T for emitter-up operation was 5.3×10³ GHz², which is about six times that of previously reported SiGe heterojunction bipolar transistors     

DC and RF performance of LP-MOCVD grownAl0.25Ga0.75As/InxGa1-xAs(x=0.15-0.28) P-HEMT's with Si-delta doped GaAs layer

Si-delta-doped Al_0.25Ga_0.75As/In_xGa_1-xAs (x=0.15-0.28) P-HEMT's, prepared by LP-MOCVD, are investigated. The large conduction band discontinuity leads to 2-DEG density as high as 2.1×10¹²/cm² with an electron mobility of 7300 cm²/V·s at 300 K. The P-HEMT's with 0.7×60 μm gate have a maximum extrinsic transconductance of 380 mS/mm, and a maximum current density of 300 mA/mm. The S-parameter measurements indicate that the current gain and power gain cutoff frequencies are 30 and 61 GHz, respectively, The RF noise characteristics exhibit a minimum noise figure of 1.2 dB with an associated gain of 10 dB at 10 GHz. Due to the efficient doping technique, the electron mobility and transconductance obtained are among the best reported for MOCVD grown P-HEMT's with the similar structure     

Fabrication of high-performance AlxGa1-xAs/InyGa1-yAs/GaAs resonant tunneling diodes using amicrowave-compatible technology

A microwave-compatible process for fabricating planar integrated resonant tunneling diodes (RTDs) is described. High-performance RTDs have been fabricated using Al_xGa_1-xAs/In_y Ga_1-yAs/GaAs strained layers. Peak-to-valley current ratios (PVRs) of 4.8:1 with simultaneous peak current densities of 4×10⁴ A/cm² have been achieved at room temperature for diodes of area 9 μm². Accurate measurements of reflection gain versus frequency between 1.5 and 26.5 GHz in the negative differential region indicate that the present technology is promising for millimeter-wave integrated circuits including self-oscillating mixers, frequency multipliers, and detectors     

GaAs/AlxGa1-xAs superlattice waveguideabsorption modulators with very low drive voltage

The first GaAs/Al_xGa_1-xAs superlattice waveguide absorption modulators operating at ~860 nm that utilize the Wannier-Stark effect are reported. The n=-1 Stark ladder peak, which is the transition from the valence band well to the nearest neighbor conduction band well, is used. This peak shifts rapidly with applied electric field, resulting in drive voltages lower than can be achieved using the quantum-confined Stark effect for quantum-well waveguides of similar structure. For a 1000-μm-long waveguide at 867 nm, the authors obtain an extinction ratio of ~20 dB and a 4-dB attenuation with a drive voltage of 2 V     

Femtosecond studies of intervalley scattering in GaAs and AlxGa1-xAs

Results are presented from ensemble Monte Carlo simulations of the relaxation of photoexcited electrons and holes. The results are compared directly with three types of femtosecond optical experiments: transient absorption saturation, pump and continuum probe, and tunable pump-probe experiments. For these experiments we find that intervalley scattering has a dominant effect for the first several hundred femtoseconds, and that electron-electron scattering is only important at later times.