Limits to normal incidence electroabsorption modulation inGaAs/(GaAl)As multiple quantum well diodes

The achievable electroabsorption modulation in GaAs/(GaAl)As normal-incidence multiple-quantum-well (MQW) diodes with 50-Å and 100-Å well widths is assessed. It is suggested that modulation performance should be characterized by the transmission change (T _hi-T_lo) when the device is used in a simple source-modulator-detector communication link, whereas in more complex applications in which optical signals are merged, the contrast is more appropriate. For either transmission change or contrast there is an optimum number of wells which varies with design voltage, and this is used to calculate achievable modulation in the bias-absorbing mode for 100-Å and 50-Å well widths. The effects of improved smoothness at the interfaces and lower background dopings are investigated. It is found that a transmission change of 40% at 5 V is typical and does not improve significantly with better growth, while the achievable contrast depends strongly on the background doping. The results are compared with those of real modulators     

Low-threshold InGaAs/GaAs strained-layer surface emitting laserswith two 45° angle etched total reflection mirrors

Summary form only given. An InGaAs/GaAs strained-layer IPSEL (in-plane surface emitting laser) structure with two 45° dry-etched mirrors and a highly reflecting bottom quarter-wavelength stack is reported. It has a record low continuous-wave (CW) threshold current at 10 mA. The laser structure consists of a conventional double-heterostructure single-quantum-well (80-Å In_0.2Ga_0.8As/100-Å GaAs) laser structure on top of a quarter-wave stack (25 pairs of 695-Å GaAs/830-Å AlAs), which serves as a distributed Bragg reflector (~99%) after 45° angle etching     

Low-temperature fabrication of p+-n diodes with300-Å junction depth

Gas immersion laser doping (GILD) was used to fabricate p⁺ -n diodes with 300-Å junction depth. These diodes exhibit ideality factors of 1.01-1.05 over seven decades of current, reverse leakage current densities ⩽10 nA/cm² at -5-V reverse bias, breakdown voltages above 100 V, and electrical activation of the boron impurity to concentrations approaching 1×10²¹ atoms/cm³. This behavior is achieved without the use of a furnace or rapid thermal anneal     

Electrical characteristics of ferroelectric PZT thin films for DRAMapplications

Ferroelectric lead zirconate titanate (PZT) films with as much as 2.5 times the storage capacity of the best reported silicon oxide/nitride/oxide (ONO) stacked dielectrics have been fabricated. A 2000-Å film with an effective SiO₂ thickness of 10 Å is demonstrated. Because of the extremely high dielectric constant (ϵ_r≳>1000), even larger storage capacities can be obtained by scaling the ferroelectric film thickness, whereas the thickness of ONO films is limited by direct tunneling through the film. Electrical conduction in the PZT films studied is ohmic at electric fields below 250 kV/cm and follows an exponential field dependence at higher fields, which is shown to be consistent with a simple model for electronic hopping through the film. Leakage current as low as 9×10^-8 A/cm² at 2.5 V for a 4000-Å film is obtained with the addition of La and Fe to compensate for Pb and O vacancies in the film. Further improvement in both leakage current and time-dependent dielectric breakdown characteristics are necessary to ensure reliable DRAM operation     

Multigigahertz CMOS dual-modulus prescaler IC

A low-power CMOS dual-modulus (divide-by-128/129) prescaler IC is described. The IC has been fabricated with symmetric CMOS technology that optimizes simultaneously the characteristics of both the p-channel and n-channel transistors for low-power-supply-voltage operation. Two different gate oxide thicknesses of 175 and 100 Å have been used. The best prescalar fabricated with 175-Å gate oxide functions at 2.06 GHz with 25-m W power consumption (L_eff=0.5 μm; V_dd=3.5 V). Preliminary results for prescalars fabricated with 100-Å gate oxide show that 4.2-GHz operation is possible (L_eff=0.4 μm; V _dd=3.5 V). Power-supply voltage as low as 1.7 V can be used for the prescalar to function at 1 GHz with a power consumption of only 4 mW     

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     

Power performance of InP-based single and double heterojunctionbipolar transistors

The microwave and power performance of fabricated InP-based single and double heterojunction bipolar transistors (HBTs) is presented. The single heterojunction bipolar transistors (SHBTs), which had a 5000 Å InGaAs collector, had BV_CEO of 7.2 V and J_Cmax of 2×10⁵ A/cm². The resulting HBTs with 2×10 μm² emitters produced up to 1.1 mW/μm2 at 8 GHz with efficiencies over 30%. Double heterojunction bipolar transistors (DHBTs) with a 3000-Å InP collector had a BV_CEO of 9 V and J_{c max} of 1.1×10⁵ A/cm², resulting in power densities up to 1.9 mW/μm² at 8 GHz and a peak efficiency of 46%. Similar DHBTs with a 6000 Å InP collector had a higher BV_CEO of 18 V, but the J _{c max} decreased to 0.4×10⁵ A/cm² due to current blocking at the base-collector junction. Although the 6000 Å InP collector provided higher f_max and gain than the 3000 Å collector, the lower J_{c max} reduced its maximum power density below that of the SHBT wafer. The impact on power performance of various device characteristics, such as knee voltage, breakdown voltage, and maximum current density, are analyzed and discussed     

Operating characteristics of InGaAs-GaAs MQW hetero-nipi waveguidemodulators

We report frequency response measurements of optical MQW nipi waveguide modulators, observing a -3-dB bandwidth as high as 110 MHz. These devices have only 900-Å-thick intrinsic regions, and thus can achieve very high fields with modest reverse bias voltages. We also measured absorption modulation (32 dB) and a phase change figure of merit as low as V_π×L=0.8 V mm at a detuning of 115 meV below the photoluminescence peak. We compare ion-implanted selective contacts with traditional selective metal contacts     

Comparison of In0.5Ga0.5P/GaAs single- anddouble-heterojunction bipolar transistors with a carbon-doped base

A comparison of MOCVD-grown, n-p-n In_0.5Ga_0.5P/GaAs single- and double-heterojunction bipolar transistors (SHBTs and DHBTs) with a carbon-doped base is presented. A base doping level of 2.5×10¹⁹ cm^-3 was employed in both device structures, resulting in a base sheet resistance of 500 Ω/sq. Common-emitter current gains as high as 210 and 150 were measured for the SHBTs and DHBTs, respectively. Results of a DC performance optimization study indicate that a 15- and 25-Å undoped set-back layer at the emitter-base junction provides optimal common-emitter current gain. The DHBTs exhibited a 40% improvement in common-base breakdown voltage compared to SHBTs (25 versus 18 V), indicating that In_0.5Ga_0.5P/GaAs DHBTs may prove suitable for power device applications     

GaAs bipolar transistors with a Ga0.5In0.5Phole barrier layer and carbon-doped base grown by MOVPE

GaAs bipolar transistors with a 50-Å-thick lattice matched Ga_0.5In_0.5P layer between the emitter and base acting as a hole repelling potential barrier in the valence band were fabricated from films grown by metalorganic vapor phase epitaxy (MOVPE). The 1000-Å-thick base was doped with carbon to 2×10¹⁹ cm^-3, resulting in a base sheet resistance of 250 Ω/□. Carbon has been chosen because of its low diffusivity. Using the barrier layer as an etch stop the authors fabricated mesa-type broad-area devices. The output characteristics of the devices are ideal with very small offset voltages and infinite Early voltages. Common emitter current gains of up to 70 at 10⁴ A/cm² collector current density were obtained. The current gain is clearly higher than the one calculated for a bipolar junction transistor with the same doping profile because the base-emitter hole current is suppressed by the Ga_0.5In_0.5P potential barrier in the valence band     

Electroabsorptive Fabry-Perot reflection modulators with asymmetricmirrors

A normally-on electroabsorptive surface-normal Fabry-Perot reflection modulator is reported with an on/off ratio of 22, insertion loss of 3.7 dB, and bandwidth of 3.4 nm for an operating voltage swing of 11 V. The asymmetric Fabry-Perot structure is made with asymmetric mirrors using a quarter-wavelength grating of 15 1/2-periods on the bottom and an air-semiconductor interface on the top. The active region is 1.4 μm thick and composed of 100Å GaAs/100 A Al_0.2Ga_0.8As multiple quantum wells. The structure provides both high-efficiency and bandwidth for surface-normal modulators     

A selective epitaxial SiGe/Si planar photodetector for Si-basedOEIC's

A P-i-N SiGe/Si superlattice photodetector with a planar structure has been developed for Si-based opto-electronic integrated circuits. To make the planar structure, a novel SiGe/Si selective epitaxial growth technology which uses cold wall ultrahigh-vacuum/chemical vapor deposition has been newly developed. The P-i-N planar SiGe/Si photodetector has an undoped 30-Å Si_0.9Ge_0.1/320-Å Si, 30 periods, superlattice absorption layer, a 0.1-μm P-Si buffer layer, and a 0.2-μm P⁺-Si contact layer on a bonded silicon-on-insulator (η_ext). The bonded SOI is used to increase the external quantum efficiency (η_ext) of the photodetector. Moreover, a 63-μm deep/128-μm wide trench, to achieve simple and stable coupling of an optical fiber to the photodetector, is formed in the silicon chip. The P-i-N planar photodetector exhibits a high η_ext of 25-29% with a low dark current of 0.5 pA/μm² and a high-frequency photo response of 10.5 GHz at λ=0.98 μm     

High-current-gain small-offset-voltage In0.49Ga0.51P/GaAs tunneling emitter bipolar transistors grown by gas sourcemolecular beam epitaxy

Different emitter size, self-aligned In_0.49Ga_0.51 P/GaAs tunneling emitter bipolar transistors (TEBTs) grown by gas source molecular beam epitaxy (GSMBE) with 100-Å barrier thickness and 1000-Å p⁺(1×10¹⁹ cm^-3) base have been fabricated and measured at room temperature. A small-signal current gain of 236 and a small common-emitter offset voltage of 40 mV were achieved without any grading. It is found that the emitter size effect on current gain was reduced by the use of a tunnel barrier. The current gain and the offset voltage obtained were the highest and lowest reported values to date, respectively, in InGaP/GaAs system heterojunction bipolar transistors (HBTs) or TEBTs with similar base dopings and thicknesses     

High-contrast/low-voltage normally on InGaAs/AlGaAs asymmetricFabry-Perot modulator

An asymmetric Fabry-Perot cavity modulator is proposed with a 50-period In_0.15Ga_0.85As/Al_0.30Ga_0.70 As strained-layer superlattice active layer. The back Bragg reflector consists of 25 periods of GaAs/AlAs layers while for the front reflector of the device the natural reflection of the air-semiconductor interface was used. Spectral measurements as a function of the applied reverse voltages showed a change in reflectivity from 33% for 0 V reverse bias to 5% for 7 V, at a wavelength of 969 nm. This gives a maximum contrast ratio of 8.3 dB and an insertion loss of 4.9 dB. For higher voltages applied across the device, the reflectivity increases again     

Transistor performance and electron transport properties of highperformance InAs quantum-well FET's

A novel field-effect transistor based on a pseudomorphic InAs quantum well in a doped InGaAs/InAlAs double heterostructure is reported. Low-field mobility, electron peak velocity, and transistor performance are studied as functions of InAs quantum well thickness, where the InAs layer is in the center of a 300-Å uniformly doped InGaAs/InAlAs quantum well lattice matched to InP. Electron transport-both at low and high fields-along with transistor transconductance are optimal for structures with a 30-Å InAs quantum well. Transistors based on the InAs quantum well structures with 0.5-μm gate lengths yielded room temperature extrinsic transconductances of 708 mS/mm, more than a 100% increase over those with no InAs     

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     

High-gain, low offset voltage, and zero potential spike byInGaP/GaAs δ-doped single heterojunction bipolar transistor(δ-SHBT)

We report on fabrication, characterization, and comparison of InGaP/GaAs single heterojunction bipolar transistors (SHBT's) and heterostructure-emitter bipolar transistors (HEBT's). The SHBT with a δ-doped sheet located at the E-B heterointerface (δ-SHBT) exhibits a common-emitter current gain as high as 410 and an extremely low offset voltage of 55 mV. Even though at the small collector current density of 1×10^-3 A/cm², the current gain is still larger than 20. Theoretical derivations show that the zero potential spike exists near the E-B junction under +1.5 V forward bias. However, an HEBT with a 700-Å narrow energy-gap emitter shows a small current gain and a collector current density due to the charge storage and bulk recombination effect. On the other hand, the increase of the CB capacitance in our δ-SHBT is very small as compared with conventional HBT's     

A low-voltage, high-reflectance-change normally off refractiveGaAs/Al0.2Ga0.8As MQW reflection modulator

We present our optimization of a normally off refractive GaAs/Al _xGa_1-xAs multiple-quantum-well (MQW) reflection modulator with respect to the on/off reflectance change, on/off contrast ratio, and operating voltage. We use optical transfer matrices, theoretically calculated refractive indices, and absorption coefficients to simulate the operation of a normal-incident Fabry-Perot MQW modulator. Our calculations suggest that a normally off refractive GaAs/Al_0.2Ga_0.8As MQW reflection modulator with a reflectance change of 42.9% and an on/off contrast ratio of 1539 for an operating voltage of only 2.44 V can be fabricated by molecular-beam epitaxy (MBE)     

Silicon-germanium base heterojunction bipolar transistors bymolecular beam epitaxy

The devices were fabricated using molecular-beam epitaxy (MBE), low-temperature processing, and germanium concentrations of 0, 6%, and 12%. The transistors demonstrate current gain, and show the expected increase in collector current as a result of reduced bandgap due to Ge incorporation in the base. For a 1000-Å base device containing 12% Ge, a six-times increase in collector current was measured at room temperature, while a 1000-times increase was observed to 90 K. The temperature dependence of the collector current of the Si_0.88Ge_0.12 base transistor is consistent with a bandgap shrinkage in the base of 50 meV. For the homojunction transistors, base widths as thin as 800 Å were grown, corresponding to a neutral base width of no more than 400 Å     

Engineering of the nonradiative transition rates inmodulation-doped multiple-quantum wells

The feasibility of the enhancement of the acoustic-phonon limited intersubband transition rate through impurity scattering has been theoretically investigated in double asymmetric-coupled quantum wells. The dependence of the acoustic-phonon rate on the barrier thickness and the effect of the position of the δ-doped region on the impurity rate have been treated rigorously. A 10-Å-doped region with a 10 ¹⁰-cm^-2-sheet density can enhance the acoustic-phonon transition limit by more than an order of magnitude. This allows for the design of intersubband lasers in which population inversion between acoustic-phonon limited discrete conduction-band states is achieved by impurity scattering and control of barrier thickness