Optical and microwave performance of GaAs-AlGaAs and strained layerInGaAs-GaAs-AlGaAs graded index separate confinement heterostructuresingle quantum well lasers

GaAs-AlGaAs and strained layer In_0.3Ga_0.7As-GaAs-AlGaAs GRINSCH SQW lasers grown by molecular beam epitaxy are discussed. The strained-layers have threshold currents of 12 mA for 30-μm×400-μm devices (1000 A/cm²) and threshold current densities of 167 A/cm² for 150-μm×800-μm devices. The threshold currents of strained-layer InGaAs lasers are lower than those of GaAs for all dimensions tested with 20-μm-wide GaAs devices exhibiting threshold currents three times those of In_0.3Ga_0.7As devices. Microwave modulation of 10-μm×500-μm strained-layer lasers with simple mesa structures yields bandwidths of 6 GHz. For all dimensions tested, strained-layer InGaAs devices have greater bandwidths than GaAs devices. These measurements confirm theoretical predictions of the effects of valence band modification due to biaxially compressive strain     

Logic Suitability of 50-nm In0.7 Ga0.3As HEMTs for Beyond-CMOS Applications

We have experimentally studied the suitability of nanometer-scale In_0.7Ga_0.3As high-electron mobility transistors (HEMTs) as an n-channel device for a future high-speed and low-power logic technology for beyond-CMOS applications. To this end, we have fabricated 50- to 150-nm gate-length In_0.7Ga_0.3As HEMTs with different gate stack designs. This has allowed us to investigate the role of Schottky barrier height (Phi_B) and insulator thickness (t_ins) on the logic characteristics of In_0.7Ga_0.3As HEMTs. The best 50-nm HEMTs with the highest Phi_B and the smallest t_ins exhibit an I_ON/I_OFF ratio in excess of 10⁴ and a subthreshold slope (S) below 86 mV/dec. These nonoptimized 50-nm In_0.7Ga_0.3As HEMTs also show a logic gate delay (CV/I) of around 1 ps at a supply voltage of 0.5 V, while maintaining an I_ON/I_OFF ratio above 10⁴, which is comparable to state-of-the-art Si MOSFETs. As one of the alternatives for beyond-CMOS technologies, we believe that InAs-rich InGaAs HEMTs hold a considerable promise.     

Dependence of differential quantum efficiency on the confinementstructure in InGaAs/InGaAsP strained-layer multiple quantum-well lasers

An internal efficiency of 91% was obtained with In_0.7Ga _0.3As/InGaAsP strained-layer multiple quantum well (MQW) lasers emitting at a wavelength of 1.5 μm. The dependence of the reciprocal differential quantum efficiency on the length of the laser cavity shows that the absorption loss in the InGaAsP (λ=1.3 μm) confinement layer caused by carrier overflowing into the confinement layer reduces the internal efficiency     

Reliability of InAlGaAs strained-quantum-well lasers operating at0.81 μm

Preliminary reliability studies of strained In_0.15Al _0.13Ga_0.72As quantum-well lasers operating at 0.81 μm are reported. InAlGaAs lasers, a possible replacement for AlGaAs lasers, have been studied with respect to three failure mechanisms. Uncoated In_0.15Al_0.13Ga_0.72As quantum-well lasers have exhibited catastrophic optical damage limits of 1.87 MW/cm², which is equal to that of similar AlGaAs lasers. Further, the lasers are both free of <100> DLD-induced sudden failures and exhibit low degradation rates even in this early stage of their development     

Self-assembled In0.5Ga0.5As quantum-dotlasers with doped active region

Self-assembled In_0.5Ga_0.5As quantum-dot lasers with different doping schemes in the active region are investigated. Their lasing wavelength, characteristic temperature, quantum efficiency, and internal loss are characterized and correlated with the size, uniformity, and density of the quantum dots as revealed by atomic force microscopy. Continuous-wave operation of Be-doped quantum-dot lasers has been achieved. Undoped In_0.5Ga_0.5 As quantum-dot lasers with a characteristic temperature as high as 125 K above room temperature have also been demonstrated     

Electrical characteristics of an optically controlled N-channelAlGaAs/GaAs/InGaAs pseudomorphic HEMT

Electrical characteristics of an n-channel Al_0.3Ga_0.7As/GaAs/In_0.13Ga_0.87 As pseudomorphic HEMT (PHEMT) with L_g=1 μm on GaAs are characterized under optical input (P_opt). Gate leakage and drain current have been analyzed as a function of V_GS, V _DS, and P_opt. We observed monotonically increasing gate leakage current due to the energy barrier lowering by the optically induced photovoltage, which means that gate input characteristics are significantly limited by the photovoltaic effect. However, we obtained a strong nonlinear photoresponsivity of the drain current, which is limited by the photoconductive effect. We also proposed a device model with an optically induced parasitic Al_0.3Ga_0.7As MESFET parallel to the In_0.13Ga_0.87As channel PHEMT for the physical mechanism in the drain current saturation under high optical input power     

High quantum efficiency and narrow absorption bandwidth of thewafer-fused resonant In0.53Ga0.47As photodetectors

We demonstrate greater than 90% quantum efficiency in an In_0.53Ga_0.47As photodetector with a thin (900 Å) absorbing layer. This was achieved by inserting the In_0.53 Ga_0.47As/InP epitaxial layer into a microcavity composed of a GaAs/AlAs quarter-wavelength stack (QWS) and a Si/SiO₂ dielectric mirror. The 900-Å-thick In_0.53 Ga_0.47As layer was wafer fused to a GaAs/AlAs mirror, having nearly 100% power reflectivity. A Si/SiO₂ dielectric mirror was subsequently deposited onto the wafer-fused photodiode to form an asymmetric Fabry-Perot cavity. The external quantum efficiency and absorption bandwidth for the wafer-fused RCE photodiodes were measured to be 94±3% and 14 nm, respectively. To our knowledge, these wafer-fused RCE photodetectors have the highest external quantum efficiency and narrowest absorption bandwidth ever reported on the long-wavelength resonant-cavity-enhanced photodetectors     

Low threshold current high-temperature operation of InGaAs/AlGaAsstrained-quantum-well lasers

The authors report improved high-temperature characteristics for In_0.2Ga_0.8As strained-quantum-well ridge waveguide lasers with an optimized cavity design. They have fabricated In_0.2 Ga_0.8As lasers that operate CW at up to 220°C with over 9-mW output power. At 200°C the threshold current is as low as 15.9 mA for a 400-μm-long laser with 35/98% reflectivity facets. Optimization of the laser cavity also improves the high-temperature operation of quantum-well lasers in other material systems; GaAs quantum well lasers that operate at up to 220°C CW have been fabricated     

Single- and double-heterojunction pseudomorphic In0.5(Al0.3Ga0.7)0.5P/In0.2Ga0.8As high electron mobility transistors grown by gas sourcemolecular beam epitaxy

In_0.5(Al_0.3Ga_0.7)_0.5 P/In_0.2Ga_0.8As single- and double-heterojunction pseudomorphic high electron mobility transistors (SH-PHEMTs and DH-PHEMTs) on GaAs grown by gas-source molecular beam epitaxy (GSMBE) were demonstrated for the first time. SH-PHEMTs with a 1-μm gate-length showed a peak extrinsic transconductance g_m of 293 mS/mm and a full channel current density I_max of 350 mA/mm. The corresponding values of g_m and I_max were 320 mS/mm and 550 mA/mm, respectively, for the DH-PHEMTs. A short-circuit current gain (H₂₁) cutoff frequency f_T of 21 GHz and a maximum oscillation frequency f_max of 64 GHz were obtained from a 1 μm DH device. The improved device performance is attributed to the large ΔE_c provided by the In_0.5(Al_0.3Ga_0.7)_0.5P/In _0.2Ga_0.8As heterojunctions. These results demonstrated that In_0.5(Al_0.3Ga_0.7)_0.5P/In _0.2Ga_0.8As PHEMT's are promising candidates for microwave power applications     

Low-threshold current density 1.3-μm InAs quantum-dot laserswith the dots-in-a-well (DWELL) structure

The wavelength of InAs quantum dots in an In_0.15Ga_0.85As quantum-well (DWELL) lasers grown on a GaAs substrate has been extended to 1.3-μm. The quantum dot lasing wavelength is sensitive to growth conditions and sample thermal history resulting in blue shifts as much as 73 nm. The room temperature threshold current density is 42.6 A cm^-2 for 7.8-mm cavity length cleaved facet lasers under pulsed operation     

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     

Quantum-well Hall devices in Si-delta-dopedAl0.25Ga0.75As/GaAs and pseudomorphic Al0.25Ga0.75As/In0.25Ga0.75As/GaAsheterostructures grown by LP-MOCVD: performance comparisons

Characterized herein are quantum-well Hall devices in Si-delta-doped Al_0.25Ga_0.75As/GaAs and pseudomorphic Al_0.25Ga_0.75As/In_0.25Ga _0.75As/GaAs heterostructures, grown by low-pressure metal organic chemical vapor deposition method. The Si-delta-doping technique has been applied to quantum-well Hall devices for the first time. As a result high electron mobilities of 8100 cm^-2/V·s with a sheet electron density of 1.5×10¹² cm^-2 in Al_0.25Ga_0.75As/In_0.25Ga_0.75 As/GaAs structure and of 6000 cm^-2/V·s with the sheet electron density of 1.2×10¹² cm^-2 in Al_0.25Ga_0.75As/GaAs structure have been achieved at room temperature, respectively. From Hall devices in Al_0.25Ga_0.75As/In_0.25Ga_0.75 As structure, the product sensitivity of 420 V/AT with temperature coefficient of -0.015 %/K has been obtained. This temperature characteristic is one of the best result reported. Additionally, a high signal-to-noise ratio corresponding to the minimum detectable magnetic field of 45 nT at 1 kHz and 75 nT at 100 Hz has been attained. These resolutions are among the best reported results     

In0.52Al0.48As/In0.53Ga0.47As double-heterojunction p-n-p bipolar transistors grown bymolecular beam epitaxy

P-n-p In_0.52Al_0.48As/In_0.53Ga_0.47 As double-heterojunction bipolar transistors with a p⁺-InAs emitter cap layer grown by molecular-beam epitaxy have been realized and tested. A five-period 15-Å-thick In_0.53Ga_0.47As/InAs superlattice was incorporated between the In_0.53Ga_0.47As and InAs cap layer to smooth out the valence-band discontinuity. Specific contact resistance of 1×10^-5 and 2×10^-6 Ω-cm² were measured for nonalloyed emitter and base contacts, respectively. A maximum common emitter current gain of 70 has been measured for a 1500-Å-thick base transistor at a collector current density of 1.2×10³ A/cm². Typical current gains of devices with 50×50-μm² emitter areas were around 50 with ideality factors of 1.4     

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     

Low-bias-current direct modulation up to 33 GHz inInGaAs/GaAs/AlGaAs pseudomorphic MQW ridge-waveguide lasers

Modulation bandwidths of 24 GHz (I_bias=25 mA) and 33 GHz (I_bias=65 mA) are demonstrated for 3×100 μm² In_0.35Ga_0.65As/GaAs multiple quantum well ridge-waveguide lasers with undoped and p-doped active regions, respectively. These performance enhancements have been achieved both by lowering the growth temperature of the high-Al-mole-fraction cladding layers and by utilizing short-cavity devices, fabricated with dry-etched facets using chemically-assisted ion-beam etching. Both the undoped and p-doped lasers also demonstrate modulation current efficiency factors exceeding 5 GHz/mA^1/2, the best reported results for any semiconductor laser     

Low temperature microwave characteristics of 0.1 μm gate-lengthpseudomorphicIn0.52Al0.48As/InxGa1-xAs(x=0.85 and 0.95) MODFET's

We have studied the microwave characteristics of 0.1 μm gate-length pseudomorphic In_0.52Al_0.48As/In_x Ga_1-xAs (x=0.85 and 0.95) modulation-doped field-effect transistors (MODFET's) at 300 K and lower temperatures down to 77 K. A maximum f_T of 151 GHz has been measured for a 0.1×55 μm² gate In_0.52Al_0.48As/In_0.85 Ga_0.15As MODFET at 77 K and this represents an improvement of 33% over the room temperature value. This behavior has been analyzed     

Comparison of steady-state and transient characteristics oflattice-matched and strained InGaAs-AlGaAs (on GaAs) and InGaAs-AlInAs(on InP) quantum-well lasers

Numerical techniques are developed to study the output spectra and to solve the multimode coupled rate equations including transverse electric (TE) and transverse magnetic (TM) propagations for In_x Ga_1-xAs-Al_0.3Ga_0.7As and In_0.53+xGa_0.47-xAs-Al_0.48In_0.52 quantum-well lasers. Optical properties are calculated from a 4×4 k×p band structure, and strain effects are included with the deformation potential theory. It is found that an introduction of 1.4% compressive strain to the quantum well results in roughly 3-4 times improvement in the intrinsic static characteristics in terms of lower threshold current, greater mode suppression and lower nonlasing photon population in the laser cavity. The authors identify the effect of strain on the large signal temporal response. They also include calculated CHSH Auger rates in their model     

Long-Wavelength Quantum-Dot Infrared Photodetectors With Operating Temperature Over 200 K

We demonstrate the high-temperature operation of confinement enhanced dots-in-a-well (CE-DWELL) quantum-dot infrared photodetectors (QDIPs). The thin Al_0.3Ga_0.7As barrier layer added above the InAs QDs greatly improve the lateral confinement of QD states in the In_0.15Ga_0.85As DWELL structure and the device performance. With better device parameters of CE-DWELL, it is possible to achieve high quantum efficiency, high operating temperature, and long-wavelength detection at the same time.     

Electroabsorption in lattice-matched InGaAlAs-InAlAs quantum wellsat 1.3 μm

Electroabsorption properties of (In_0.53Ga_0.47As)_0.7 (In_0.52Al_0.48As)_0.3-In_0.52Al _0.48As quantum wells were investigated experimentally and analytically in order to form a semi-empirical model for 1.3 μm optical modulator applications. The observed exciton energy shifts and changes in electron-hole wave function overlap integrals are in agreement with calculation for the quantum confined Stark effect. Empirically, we found that the room-temperature exciton absorption peak can be described by a Gaussian peak, and that the residual absorption should be characterized by an exponential tail. In order to provide realistic linewidth broadening parameters, empirical expressions are summarized here for this material     

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