Ga1-yInyAs/InAsxP1-1 (y>0.53, x>0) pin photodiodes for long wavelengthregions (λ>2 μm) grown by hydride vapour phase epitaxy

pin photodiodes with a 2.3 μm absorption edge are presented, using hydride vapour phase epitaxy. A Ga₁-_yIn_yAs (y=0.72) absorption layer, lattice-mismatched to the InP substrate, was grown on an InAs_xP_1-x (x=0-0.33) graded composition buffer layer. Typical dark current was 5 μA (0.03 A/cm²) at -6 V. Effective carrier lifetime of 0.05 μs was estimated from I/V characteristics     

Hg1-xCdxTe metal-semiconductor-metal (MSM)photodetectors

Metal-semiconductor-metal (MSM) detectors with active layers of Hg _1-xCd_xTe (x=0.62-0.74) and electrode spacings of 2, 4, and 6 μm have been fabricated and characterized. Direct-current measurements have shown a low dark current and high responsivity from 0.15 to 1.5 A/W at 10-V bias. The lowest values of dark current (0.16 mA cm²) were obtained for detectors which incorporated an overlayer of CdTe. For detectors without the overlayer, increasing the Cd mole fraction resulted in a decrease in the dark current and a reduction in the 300-nm responsivity. Measurements of frequency response for these detectors show a maximum loss of 8 dB to 20 GHz. These results compare favorably with high-performance MSM detectors based on In_0.53Ga_0.47As with a lattice-matched barrier layer of In_0.52Al_0.48As     

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     

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-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     

Strained-insulatorInxAl1-xAs/n+-In0.53Ga0.47As heterostructure field-effect transistors

In an effort to enhance the conduction band discontinuity between channel and insulator, In_xAl_1-xAs/n⁺-In _0.53Ga_0.47As heterostructure field-effect transistors (HFETs) were fabricated with InAs mole fractions in the In _xAl_1-xAs gate insulator of x=0.52 (lattice matching), 0.48, 0.40, and 0.30. Decreasing the InAs mole fraction in the insulator results in reduced forward- and reverse-bias gate currents, increased reverse gate breakdown voltage, and reduced real-space transfer of hot electrons from channel to gate. Down to x =0.40, these improvements trade off with a slightly reduced transconductance, but the gain in gate bias swing results in an increase in maximum current drivability. From x=0.40 to x=0.30, there is a drastic decrease in transconductance, coincident with a high density of misfit dislocations     

Effect of parameter variations on the performance of GaAs/AlGaAsmultiple-quantum-well electroabsorption modulators

A theoretical investigation is presented of the dependence of electroabsorption in GaAs/Al_xGa_1-xAs multiple-quantum-well (MQW) structures on the MQW parameters (Al mole fraction x, well thickness L_z barrier thickness L_b and interface quality) and on the applied electric field studied. The on/off ratio of a modulator using MQWs with x=0.45, L_z=75 Å, and L _b=78 Å is predicted to increase by 20% compared to that of a modulator using MQWs with x=0.3, L_z =100 Å, and L_b=100 Å, when the MQW total active region thickness is 1 μm     

Long-wavelength, InAsSb strained-layer superlattice photovoltaicinfrared detectors

Long-wavelength infrared photodiodes were fabricated using InAs _1-xSb_x/InSb (x=0.82-0.85) strained-layer superlattices (SLSs). These structures can be grown using either molecular-beam epitaxy or metalorganic chemical vapor deposition. These photodiodes display broad spectral responses up to wavelengths greater than or approximately equal to 10 μm, and detectivities of 1×10 ⁹ cm-Hz^1/2/W at 10 μm     

Monte Carlo study of GaAs/Alx Ga1-xAsMODFETs: effects of AlxGa1-xAs composition

Monte Carlo methods are used to compare electronic transport and device behavior in n⁺-Al_xGa_1-xAs/GaAs modulation-doped field-effect transistors (MODFETs) at 300 K for x =0.10, 0.15, 0.22, 0.30, 0.35, and 0.40. The differences between the x=0.22 and x=0.30 MODFETs with respect to parasitic conduction in Al_xGa_1-xAs, gate currents, and switching times, are of particular interest. The donor-related deep levels in Al_xGa_1-xAs, are disregarded by assuming all donors to be fully ionized, and the focus is only on the confinement and transport of the carriers. The following quantities are studied in detail: transfer characteristics (I_D versus V _G), transconductance (g_m), switching speeds (τ_ON), parasitic conduction in Al_xGa _1-xAs, gate current (I_G), average electron velocities and energies in GaAs and Al_xGa_1-x As, electron concentration in the device domain, k-space transfer (to low mobility L and X valleys), and details of the real-space transfer process     

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     

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     

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     

Schottky diodes of Au on GaAs1-xSbx/GaAs n-Nheterostructures grown by MBE

Au Schottky barrier heights on molecular-beam-epitaxial grown n-GaAs_1-xSb_x/N-GaAs heterostructures with x up to 0.26 have been studied. It was found that φ_bn=0.9-1.77x+2.89x², or φ_bn≈0.77E_g-0.20 for x<0.26. The pinning position of the Fermi level with respect to the valence-band edge for x<0.26 takes the form of E _pin=-0.52x+0.53 eV, which also appears to be valid for an x value up to 1.0     

The refractive index near the fundamental absorption edge inAlxGa1-xAs ternary compound semiconductors

The real part of the complex refractive index is calculated for photon energies over the region from 1.2 to 1.8 eV for Al_xGa _1-xAs compounds as a function of x. No singularity is predicted. Rather, a change in the functional form of the refractive index, n occurs as the photon energy passes through the bandgap energy, G, leading to a local maximum or, more accurately, a plateau region in n as a function of frequency, which is observed experimentally. The effect of a finite-spin orbit-splitting energy and the effect of higher conduction bands are included. Theoretical and experimental results are compared for Al_xGa _1-xAs over a range of mole fractions from x=0 to x=0.198     

High-transconductance heterostructure Ga0.47In0.53As/InP metal-insulator-semiconductor field-effect transistorsgrown by chemical beam epitaxy

SiO₂ insulator is on top of an InP layer; current transport occurs, however, an in adjacent n-type Ga_0.47In_0.53As:Sn layer. A transconductance of g_m=300 mS/mm is obtained from depletion-mode MISFETs with a gate length of 1.2 μm. This MIS (metal-insulator-semiconductor) junction has a symmetric current-voltage characteristic and a low-leakage current of ~1 nA at ±2 V. High-frequency S-parameter measurements performed b probing devices on the wafers yield a unity current gain frequency of F _t=22.2 GHz and a maximum frequency of oscillation f _max=27 GHz     

Theoretical and experimental studies of the effects of compressiveand tensile strain on the performance of InP-InGaAs multiquantum-welllasers

The authors have studied, both theoretically and experimentally, the effects of biaxial strain upon the performance characteristics of broad-area InP-InGaAsP-In_xGa_1-xAs (0.33⩽x ⩽0.73) separate confinement heterostructure multiquantum-well lasers. The theoretical calculations include the effects of strain on the bandstructure and the Auger recombination rates. A pronounced dependence of the threshold current density J_th upon x is observed. The lowest measured J_th is 589 A/cm² in an 800-μm laser with x=0.68. Also, internal quantum efficiencies as high as unity and loss coefficients as low as 5.6 cm^-1 have been measured for x=0.58     

Hg0.4Cd0.6Te 1.55-μm avalanche photodiodenoise analysis in the vicinity of resonant impact ionization connectedwith the spin-orbit split-off band

The authors describe the electrical and optical characterization of three Hg_1-xCd_xTe avalanche photodiodes manufactured using planar technology with composition parameter x near 0.6. This alloy composition leads to devices that are well suited for 1.55-μm detection. From the noise analysis under multiplication, the authors show the tight dependence of the ratio β/α (of the hole; and electron ionization coefficient, respectively) upon x and the ratio Δ/E_g where Δ is the spin-orbit splitting energy and E _g is the bandgap energy. It turns out that in these alloys around x=0.6, Δ is very close to the bandgap energy so β/α reaches its maximum value. Owing to this property, which is characteristic of II-VI compounds, Hg_1-xCd_xTe is a good candidate for 1.3-μm to 1.6-μm avalanche photodiodes     

Polarization-independent strained InGaAs/InGaAlAs quantum-wellphase modulators

Polarization-independent phase modulation in In_1-xGa _xAs/InGaAlAs multiple-quantum-well waveguides is demonstrated for the first time. It is shown that by increasing the Ga fraction and hence the tensile strain in the quantum well the electric-field-induced refractive index change in the TM polarization Δn_TM can be made to approach that in the TE polarization Δn _TE. At 1.523 μm, the ratio Δn_TM /Δn_TE=1 for x=0.7 with a phase shift coefficient of 17.4°/V-mm was achieved. Polarization independence was maintained over the entire range of reverse bias voltage     

A pseudomorphic AlGaAs/n+-InGaAs metal-insulator-dopedchannel FET for broad-band, large-signal applications

Molecular beam epitaxy (MBE)-grown L_g=1.7-μm pseudomorphic Al_0.38Ga_0.62As/n⁺-In_0.15Ga _0.85As metal-insulator-doped channel FETs (MIDFETs) are presented that display extremely broad plateaus in both f_T and f_max versus V_GS, with f_T sustaining 90% of its peak over a gate swing of 2.6 V. Drain current is highly linear with V_GS over this swing, reaching 514 mA/mm. No frequency dispersion in g _m up to 3 GHz was found, indicating the absence of electrically active traps in the undoped AlGaAs pseudoinsulator layer. These properties combine to make the pseudomorphic MIDFET highly suited to linear, large-signal, broadband applications     

Characteristics of 0.8- and 0.2-μm gate length InxGa1-xAs/In0.52Al0.48As/InP(0.53⩽x⩽0.70) modulation-doped field-effect transistorsat cryogenic temperatures

The performance characteristics of InP-based pseudomorphic MODFETs with varying the In composition (0.53⩽x⩽0.70), which changes the strain in the channel, were studied. The temperature was varied in the range of 40-300 K, and the devices had gate lengths L _g of 0.8 and 0.2 μm. The analysis predicts an increase in the intrinsic cutoff frequency with increasing In composition and decreasing temperature and gate length. Also, the analysis predicts that the increase in cutoff frequency with decreasing temperature is less significant with increasing In composition and decreasing gate length. Preliminary experimental results show that as In composition increases from 0.53 to 0.70, f_T increases by 30-40%, and as the temperature decreases from 300 to 40 K, f_T improves by 15-30%, both for 0.8- and 0.2-μm devices