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High-quality multiquantum well (MQW) structures with 1.5% compressive strain in InAsP wells and 0.8% tensile strain in InGaP barriers have been grown by gas-source molecular beam epitaxy on InP substrates. High-speed (3 dB bandwidth over 10 GHz) and low driving voltage (lower than 3 V for 20 dB on/off ratio) operation using these structure is demonstrated. These characteristics are the first reported for MQW modulators operating at 1.3 /spl mu/m.

Quarter-micrometre channel doped GaInP/InGaAs HFETs with high current density show a noise figure comparable to that of PM-HEMTs (0.6 dB at 12 GHz). Owing to the high linearity of the channel doped device, the noise figure shows an extremely weak dependence on drain current and bias. The absence of DX-centres in the GaInP leads to a pure 1/f noise spectrum without Gaussian shaped generation recombination parts.

The authors report InGaAs single quantum well vertical-cavity surface-emitting lasers with an intracavity p-contact fabricated by selective oxidation of AlAs and distributed Bragg reflectors composed of binary materials (AlAs/GaAs). Record low threshold currents of 8.7 µA in ~3 µm square devices and 140 µA in 10 µm square devices with maximum output powers over 1.2 mW are achieved.

An index-guided InGaAs/GaAlAs vertical-cavity surface-emitting laser with a native oxide confinement structure has been proposed and fabricated. A record threshold current of 70 µA was achieved with a 5 µm-diameter core device. The proposed structure provides strong electrical and optical confinements. Also a reduction in nonradiative recombination and an improvement in the thermal resistance can be expected.

A novel HEMT layout with ringshaped gate is reported. This conception avoids the problems related to mesa etching at the active region and provides additional possibilities for circuit design. The layer structure of the investigated device is based on an Al-free InP/InGaAs material system. Transistors with a gate length of 0.7 µm show an fT of 40 GHz and an fmax of 117 GHz. These values are similar to results obtained with the conventional HEMT design.

The authors have demonstrated microgun-pumped blue and blue-green semiconductor lasers operating at 496 nm and 514 nm, respectively. Graded-index separate-confinement heterostructures were employed based on the CdZnSe/ZnSe material system. The corresponding lasing thresholds were in the 8-17 kW/cm/sup 2/ range for operating temperatures of 85 to 135 K. >

Selective dry etching of InGaAs over AlInAs in CH/sub 4//H/sub 2/-based ECR discharges found to produce extensive hydrogen passivation in the AlInAs donor layer of high electron mobility transistor (HEMT) structures. Hydrogen concentrations of 5*10/sup 19/ cm/sup -3/ are measured in this layer even before complete removal of the overlying InGaAs cap layer. Careful control of over-etch time is necessary to minimise passivation effects on the saturation drain-source current in the InGaAs/AlInAs HEMTs. >

Deuterium concentrations of ≥ 1021 cm-3 can be introduced into epitaxial InAlN and InAlGaN by plasma exposure at 250°C. This produces a decrease of approximately a factor of 10 in the n-type carrier concentration in these materials, but can be reversed by annealing at ~500°C. Reactivation occurs with an apparent activation energy of ~2.4 eV. Annealing at 900°C is required to remove > 90% of the deuterium from both nitride materials.

Electroabsorption optical modulators integrated with passive waveguides have been fabricated on GaAs/AlGaAs multiquantum well material using the impurity-free vacancy diffusion technique with SrF2 and SiO2 capping layers. At a wavelength of 861.6 nm, devices with a 400 µm long modulator section showed ON/OFF ratios greater than 35 dB for a reverse bias voltage of 3 V.

Continuous-wave (CW) operation of a strained InGaAs quantum disk laser with nanoscale active-structures self-organised on GaAs (311)B substrate is demonstrated at room temperature. The threshold current is ~20 mA, which is considerably lower than that of double quantum well lasers on GaAs (100) substrate grown side-by-side.

Optically pumped vertical cavity laser operation up to T = 260 K has been achieved in the 480–500 nm-wavelength range in ZnCdSe/ZnSSe/ZnMgSSe pseudomorphic separate confinement heterostructures, containing three active quantum well layers and dielectric high reflectivity mirrors.

GaAs/AIGaAs two-dimensional quantum-well wire laser arrays fabricated by metal-organic chemical vapour deposition on nonplanar substrates have realised a linear light pulse output Fewer of over 100mW. This is the highest figure reported to date for all kinds of quantum-well wire lasers.

The effect of electron cyclotron resonance (ECR) plasma etching using CH4/H2/Ar on Si δ-doped pseudomorphic AlGaAs/InGaAs/GaAs heterostructures and field-effect transistors has been investigated. Hall measurements were performed as a function of temperature (5–300 K) and the Hall mobility and the sheet density compared to wet chemically etched reference samples. Direct current and high-frequency measurements were performed on dry gate-recessed PMHFETs.

Greater than 150°C CW lasing is achieved from an unbonded GaAs/AlGaAs VCSEL by employing high barrier confinement spacers and by blue shifting the optical gain. This is done while maintaining a variation in threshold current of only ±0.93 mA over a range greater than 150°C. These results are compared to a low barrier VCSEL of similar design.

The authors report the electroabsorption response of strained multiquantum well In 0.2 Ga 0.8 As/GaAs structures as a function of increasing barrier thickness. We find that a tradeoff exists between improved structural quality and reduced performance due to the increase in nonabsorbing material. However changing the barrier from 100 to 200 A causes a 25% increase in the maximum absorption change and a significant lowering of the insertion loss

The authors have achieved CW operation of 650 nm GaInP/AlGaInP index waveguide-type visible-light laser diodes (LDs) with dry-etched mesa stripes fabricated by Cl/sub 2/ reactive ion beam etching. The threshold current of 47 mA and slope efficiency of 0.40 W/A are almost the same as those of a wet-etched LD fabricated from the same wafer (L=500 mu m). The cross-sectional scanning electron microscope view of the buried mesa stripe shows that the dry-etched LD has a symmetric mesa shape resulting in a small focusing spot and stable mode operation. The wet-etched mesa, however, is asymmetric because a 6 degrees misoriented substrate is used for this wavelength operation. An aging test with light output power of 3 mW at 50 degrees C has revealed that these LDs have an operating time of over 3000 h, which represents a sufficient reliability for conventional uses. >

A 0.65 µm gate length composite channel InP-HEMT for low bias use in mobile communication is discussed. At VD = 1.6 V a record fmax/fT = 2.6 in combination with fTLg = 39 GHzµm or 2.45 × 107 cm/s, which is essentially above the collision dominated value, is obtained. The fT is already higher than 40 GHz (fTLg = 26 GHzµm) at VD = 0.75 V with an associated fmax/fT = 1.6.

A new high-speed, waveguided InP based on the InGaAs/InAlAs multiquantum-well pin photodiode with gain and fabricated by metal organic vapour phase epitaxy is reported. The quantum-confined Stark effect can be used to tune this diode over a 250 nm range in the wavelength region around 1.55 µm. A 3 dB bandwidth of more than 12 GHz and avalanche multiplication have been observed.

Electroabsorption optical modulators have been fabricated on GaInAs/GaInAsP multiquantum well structures whose bandgap had been increased by laser photoabsorption-induced disordering. Modulation depths of 20 dB have been obtained in material which has been bandgap blue shifted by as much as 120 nm, while samples shifted by 80 nm gave depths as high as 27 dB.

The authors present experimental results which indicate that a Dy3+-doped Ga:La:S glass fibre amplifier may be operated efficiently at 1.3 µm with an optimum device length significantly shorter than a comparable Pr3+-doped glass fibre amplifier. Moreover, the efficiency exceeds that obtained from the Pr3+-doped ZBLAN devices currently available.

The authors demonstrate the direct bonding of InP/Gd3Ga5O12 (GGG) and InP/GaInSb on GGG without glue. After chemical treatment, heat treatment was applied in an H2 atmosphere without a weight. This technique makes feasible the integration of semiconductor and magneto-optic devices.

The authors report the first realisation of a two-dimensional photonic bandgap structure with a period of lambda /sub 0//2n in the GaAs/AlGaAs material system. The structure consists of a honeycomb lattice with a wall thickness of approximately 30 nm and a period of 160 nm. It was found that, to realise patterns of such small size and periodicity, it is crucial to control the shape of the exposed features.

A current gain of 120, for a base sheet resistance of 400 Omega / Square Operator , is reported in a carbon doped base heterojunction bipolar transistor grown by chemical beam epitaxy (CBE) without hydride sources. This result is to the authors' knowledge, the best obtained with hydride free CBE for this device.

CW output powers in excess of 1 W and reliable CW output powers of 250 mW at room temperature from double quantum well compressively strained GaInP/GaAlInP laser diodes with an emission wavelength of 645 nm were demonstrated. An anomalous dependence of threshold current density and wavelength on GaInP/GaAlInP laser diode stripe width was characterised.

Electroluminescence has been observed from InGaAs/InAlAs HEMTs under low bias conditions confirming the presence of holes caused by impact ionisation. The field required for the onset of electroluminescence and the kink effect are similar, suggesting that the kink effect is associated with impact ionisation.

Ballistic point contacts defined in a high-mobility two-dimensional electron gas exhibit extremely nonlinear current-voltage characteristics. This nonlinearity has been used to mix microwave signals up to frequencies of 10 GHz.

Anisotropic dry etching of GaInP/AlGaInP heterostructures has been achieved for the first time in a high-ion-density electron cyclotron resonance (ECR)-generated plasma. Structures consisting of AlInP/(GaInP/AlGaInP)/AlInP and AlGaAs/(GaInP/AlGaInP)/AlGaAs heterostructures have been etched in a CH4/H2/Cl2/BCl3/Ar plasma with smooth sidewalls and surface morphologies.

The authors report the first clear observation of Wannier-Stark localisation in an unstrained In/sub 0.15/Ga/sub 0.85/As/In/sub 0.15/Al/sub 0.85/As superlattice on a strain-relaxed InGaAs buffer layer grown on GaAs substrate. Optical bistability is demonstrated for a resistor-SEED (self-electro-optic effect device) and a symmetric SEED system at an operating wavelength of 877 nm.

The authors investigate the current-voltage characteristics of In/sub 0.3/Ga/sub 0.7/As/In/sub 0.29/Al/sub 0.71/As double-barrier resonant tunnelling diodes grown on GaAs substrates. These devices exhibit peak-to-valley current ratios as high as 7.6 and 19.5 at room temperature and 77 K, respectively. Two negative differential resistance regions are also observed for devices with larger well width. These results have shown that a high quality epilayer can be obtained despite the large lattice mismatch between In/sub 0.3/Ga/sub 0.7/As and GaAs. >

Output power of 2.26 W and maximum power conversion efficiency of 57% were obtained for InGaAs-AlGaAs strained-layer quantum-well lasers (25 degrees C, lambda approximately=1 mu m). Output powers were 2.35 W (-55 degrees C) and 1.79 W (75 degrees C) with maximum power efficiencies of 51% (-55 degrees C) and 46% (75 degrees C).

Extremely low backgating currents ( approximately 30-40 mu A) are measured in 0.1 mu m gate In/sub 0.3/Ga/sub 0.47/As/In/sub 0.52/Al/sub 0.48/As/InP MODFETs having a new buffer layer material, Er-doped In/sub 0.52/Al/sub 0.48/As, grown at 500 degrees C by MBE. Rare-earth doped GaAs and the lattice-matched ternary have resistivity approximately 10/sup 2/-10/sup 5/ Omega -cm depending on Er-doping level.

The authors report the generation of tunable, CW, X-band microwave radiation using optical mixing in an Al/sub x/Ga/sub 1-x/As optical waveguide. Two optical frequencies from CW, Nd-YAG ring lasers are mixed to obtain microwave radiation between 7 and 13 GHz.

Using MOVPE, we fabricated strained quantum well 1.3 mu m lasers with an InGaP cladding layer on a GaAs substrate. The lasers had a high gain coefficient of 60 cm/sup -1/. Lasers with high reflection facets had a low threshold current density of 500 A/cm/sup 2/, and a high characteristic temperature of 100 K.

The operation of (In,Ga)As quantum well lasers prepared on [112]-oriented GaAs substrates is reported. Threshold current densities as low as 187 A/cm2 for a 1.57 mm-long device have been obtained under pulsed-mode operation. The demonstration of laser action in a heterostructure grown on the [112]-oriented substrate is important for the design of blue-green light emitters.

The scaling to 0.5 µm of the inversion channel HFET with a single strained InGaAs quantum well is described. A unity current gain frequency of 40 GHz, gm = 205 mS/mm and VTH = –0.34 V have been obtained for 0.5 × 100 µm2 devices. For shorter gate lengths, threshold shifts are sizeable so that in order to scale further, modifications to the growth and processing are required.

Strained multiquantum-well InGaAs lasers had CW thresholds near 50 mA at 2 mu m at 312 K. Abrupt decreases in characteristic temperatures (T/sub 0/) occurred at 250 K for threshold current and 273 K for external quantum efficiency, indicating a highly temperature sensitive nonradiative recombination mechanism. >

The authors report what they believe to be the first successful fabrication of an InGaAs/GaAs vertical-cavity surface emitting laser (VCSEL) using optically transparent indium-tin-oxide (ITO) ohmic contacts to p- and n-type regions of the laser. Threshold current densities J/sub th/ are similar to those lasers fabricated from the same wafer using conventional ohmic contacts.

Reduction of intervalence band absorption found in highly strained semiconductor lasers is dominated by enhancement in the TE gain spectrum due to the inclusion of compressive strain in the active layer and not by a change in the S-like character of the spin-orbit band.

The first Al0.18Ga0.34In0.48P/GaAs/Ga0.52In0.48P double heterojunction bipolar transistors grow by metal organic vapour phase epitaxy are reported. They exhibit a current gain of 110 at high collector-emitter voltage and a small offset voltage of 30mV. The addition of Al to the emitter has not adversely affected the quality of the emitter-base interface.

A new TE-TM mode splitter with an asymmetric Y-junction structure operated by directly focusing randomly polarised light on to a titanium indiffused waveguide which is then directed to an ordinary-polarised nickel indiffusion waveguide and an extraordinary-polarised proton exchange waveguide in lithium niobate is demonstrated. The measured extinction ratio is greater than 20 dB for both TE and TM modes.

The buffer layer in AlGaN channel HEMTs to suppress the off-state drain leakage current is investigated. By employing an AlN for the buffer layer in Al 0.39 Ga 0.61 N/Al 0.16 Ga 0.84 N HEMTs, the off-state drain leakage current was sufficiently suppressed and the breakdown voltage was enhanced. It was considered that employing the AlN for the buffer layer is important for extracting the superior material properties of the AlGaN in the channel layer.

45 nm-gate AlGaN/GaN MIS-HEMTs on SiC substrates have been fabricated and their DC and RF characteristics measured at 300 and 16 K. A source-drain spacing Lsd of 1.5 µm was used to reduce parasitic resistances, which was 0.5 µm shorter than that in previous work. High cutoff frequency fT values of 156 GHz at 300 K and 194 GHz at 16 K were obtained. These fT values are about 10% higher than those of AlGaN/GaN MIS-HEMTs with an Lsd of 2 µm.

The performance of SiO/sub 2//AlGaN/GaN MOSHFETs is described. The C-V measurements showed slight increase in sheet carrier density after applying 12 nm-thick PECVD SiO/sub 2/. The devices exhibited gate leakage current of 5/spl times/10/sup -10/ A/mm. Small-signal RF characterisation of 0.7 /spl mu/m gate length devices yielded an f/sub T/ of 24 GHz and an f/sub max/ of 40 GHz, which are comparable to those typical for state-of-the-art AlGaN/GaN HFETs.

The voltage–voltage characteristic of electron Y-branch switches controlled by four independent side-gates is considered. Using one branch as a low-dimensional gate, the conductance between the stem and the other branch can be adjusted. It is found that the Coulomb repulsion of electrons in the different branches is drastically enhanced for a critical voltage range at the outer side-gates. Using the branch-gate and the outer side-gates as input stages, the voltage–voltage characteristics can be tuned to an inverted and non-inverted response, respectively, with gain and internal hysteretic switching.

An npn double heterojunction bipolar transistor has been made using In 0.27 Ga 0.73 Sb for the base and two different In x Al 1-x As y Sb 1-y alloys for the emitter and collector. It has a common emitter current gain of 25. The emitter-base voltages required for a given collector current are smaller than those of InP-based HBTs.

Using conventional photolithography, Al 0.35 Ga 0.65 N pin diodes have been fabricated that exhibit extremely low reverse bias leakage currents. Macroscopic I-V measurements from a statistical population of 64, 120 μm diameter, circular diodes gives a mean leakage current of 0.96 fA with a standard deviation of 0.90 fA at -0.5 V bias.

A comparison of RF reliability at 10 GHz on four different undoped AlGaN/GaN HEMT structures with AlGaN barrier thickness variation is presented. The output power degradation characteristics during RF stress for each structure are shown, and the results indicate a strong dependence of reliability on AlGaN thickness. A device from the structure with the thinnest AlGaN in the study, with initial output power of 8.8 W/mm at 40 V, showed only a change of 0.55 dB in output power after 185 h of RF stress at 40 V. The results demonstrate excellent RF reliability of high-power devices and the potential of stable high-power operation of undoped AlGaN/GaN HEMTs on SiC.

Antimonide-based HEMTs with a 0.35 µm gate length have been fabricated with an InAlSb/InAs heterojunction. The new Te-doped MBE material, which does not contain highly-reactive AlSb, exhibits a Hall mobility of 23,500 cm2/V-s and a sheet density of 1.7×1012 cm−2. The devices have a DC transconductance of 1000 mS/mm and an fTLg product of 32 GHz-µm at VDS=0.35 V.

The effects of RF stress on power and pulsed IV characteristics of field-plated AlGaN/GaN HEMTs fabricated on two different epitaxial structures are presented. The power degradation characteristics are shown. The RF stress resulted in different degrees of RF voltage and current swing reduction on the two wafers. The current dispersion became more aggravated after RF stress under high quiescent drain bias conditions in one of the structures.

A nonvolatile current sensing device using Pb(Zr0.52,Ti0.48)O3 (PZT) as a gate and BaRuO3 (BRO) as a thin film channel is demonstrated. A nonvolatile change of 33% in the sheet resistance of BRO has been observed as the polarisation of the ferroelectric PZT layer is reversed. This change was nonvolatile after 24 h and the conductivity measurements between 80 and 300 K revealed that the BRO layer shows n-type conduction. The BRO channel is compatible with PZT process and the all-oxide structure offers the possibility of nonvolatile, current-sensing memory devices.