GaAs Schottky diodes with near-ideal characteristics

The I-V characteristics of some GaAs Schottky-barrier IMPATT diodes are found to be nearly ideal at operating temperatures (∼200°C). Fabricated on epitaxial n-type substrate with platinum contacts, the diodes use a truncated cone shape to avoid soft breakdown. The breakdown voltage and its temperature dependence are close to calculated values for one-sided abrupt junctions.     

Electrical characteristics of GaAs MIS Schottky diodes

The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of GaAs metal-insulator-semiconductor (MIS) Schottky barrier diodes are investigated over a wide temperature range and compared with MS diodes. The effects of the insulating layer on barrier height and carrier transport are delineated by an activation energy analysis. Excess currents observed at low forward and reverse bias have also been analyzed and their cause identified. A capacitance anomaly consistently noticed in MIS Schottky barriers is resolved by stipulating a non-uniform interfacial layer, and a self-consistent model of the GaAs MIS Schottky barrier is developed by analyzing I-V and C-V data of both MIS and MS diodes.     

Numerical analysis of GaAs epitaxial-layer Schottky diodes

A computer simulation of GaAs epitaxial-layer Schottky-barrier diodes has been carried out. The present work extends previous drift-diffusion equation (DDE) Schottky-barrier diode simulations to very thin epilayers of GaAs as well as to higher forward bias voltages. Diodes having epitaxial layers of 0.12 and 1.0 µm were modeled with an emphasis on comparison with experiment. To achieve better agreement with experimental data an interfacial layer was included in the model, resulting in a voltage-dependent barrier height. The bias voltage at which the I-V characteristic becomes strongly nonideal is predicted to depend more on the potential drop across the interfacial layer than on the series resistances present in the devices studied. The separate contributions of the dynamic resistance of the junction and of the series resistances of the epitaxial and bulk regions to the total resistance were examined for forward biases up to 1.1 V.     

High reliability sputtered Schottky diodes on GaAs

We describe developments to improve reliability and power handling for high frequency applications in whisker-contacted Schottky barrier diode mixers, detectors and multipliers fabricated using sputtered refractory metals and silicides. The lift-off process has been used to fabricate diodes on GaAs with ideality factors of 1.18 and 1.06 for W/GaAs and TiSi_x/GaAs contacts respectively.     

GaAs Schottky diodes for THz mixing applications

The operation of GaAs Schottky barrier diodes, the critical mixer element used in heterodyne receivers for a variety of scientific applications in the terahertz frequency range, is reviewed. The constraints that the receiver system places on the diodes are considered, and the fundamental guidelines for device optimization are presented. The status of ongoing research, both experimental and theoretical, is examined. Emphasis is placed on investigations of the various effects that can limit diode performance at these high frequencies. Investigations of planar diode technology are summarized, and the potential replacement of whisker-contacted devices with planar structures is considered     

Traps in fast-neutron irradiated GaAs Schottky diodes

GaAs Schottky diodes were irradiated with an essentially gamma-free beam of 5 MeV neutrons and the resultant trap (and defect) structure analyzed. The trap structure is shown to consist of energetically discrete levels, but the levels are found not to operate independently. A new defect model is proposed based on coupled-trap levels and is shown to be in good agreement with the observations. On the basis of this model, the following values for discrete trap levels were determined: 175, 220, 325, 380 and 460 mV below the construction band.     

Local-oscillator-induced noise in GaAs Schottky mixer diodes

Increased noise temperature induced by local-oscillator power has been measured in Schottky-diode millimetre-wave mixers at 250 MHz and 4.75 GHz. Electric-field calculations indicate a portion of this noise is due to intervalley scattering in the undepleted epitaxial layer directly adjacent to the Schottky-diode anode. A noise-temperature equation is presented, which accounts for both shot and thermal noise, where the thermal portion includes the intervalley scaltering component.     

GaAs microlens arrays grown by shadow masked MOVPE

This paper describes the fabrication of high quality GaAs microlenses and microlens arrays using shadow masked metalorganic vapor phase epitaxial (MOVPE) growth (SMMG). Microlenses with apertures as small as 30 μm were fabricated and focal lengths down to 40 μm were measured. The smaller lenses closely fit the theoretical behavior of ideal spherical lenses while larger lenses (focal length >80 μm) showed a more complex physical shape and could not be modeled as spherical. This deviation from a spherical shape is expected from simulation of SMMG. The full width at half maximum of the beam waist was <2 μm for all sizes of microlens indicating that these lenses are compatible with coupling to single mode fibers.     

Computer study on GaAs Schottky barrier IMPATT diodes

Oscillation characteristics of GaAs Schottky barrier IMPATT diodes are studied by computer simulation. For a Schottky barrier-n-n⁺ structure, the Read condition and the just-punch-through condition are found to be optimum with respect to the efficiency and power at 30 GHz. In order to improve the efficiency, a superabrupt doping profile is proposed and a high efficiency of 32 per cent is predicted. Calculation of the frequency dependence of the efficiency shows that GaAs IMPATT diodes still have the potentiality of high efficiency oscillator at 100 GHz and they are a promising microwave source in mm-wave region.     

MOVPE InGaAs/InP grown directly on GaAs substrates

We have demonstrated the feasibility of growth of InP/InGaAs structures directly on GaAs using atmospheric pressure metal organic vapour phase epitaxy. Growth conditions and the equipment used are described along with some preliminary measurements on the GaAs/InP/InGaAs wafers. P-N junctions were formed in these materials to evaluate diode characteristics.     

Breakdown and capacitance properties of hyperabrupt epitaxial Schottky barrier diodes

An analysis of the breakdown and capacitance properties of punch-through hyperabrupt epitaxial Schottky barrier diodes has been carried out. Results are given for the dependence of breakdown voltage of such a device on surface concentration and epitaxial layer thickness. Design curves are given for epitaxial hyperabrupt schottky varactor diodes. The design procedure yields an optimal impurity profile in which just-punch-through occurs at the highest voltage of operation. This gives a maximum dynamic range of operation still keeping the series resistance to a minimum. A corrected boundary condition to determine the profile constants associated with an n/n⁺ (high/low) junction is also given.     

Capacitance-voltage characteristics of microwave Schottky diodes

Based on an analytical solution of Poisson's equation, the authors calculate/capacitances of metal circular dots and metal stripes on the surface of a doped semiconductor material. When the dimensions of the dot or stripe are much larger than the depletion region, the results are reduced to the conventional formula for a parallel-plate capacitor. In the opposite limit, the overall capacitance is determined by the edge effect. This edge capacitance is proportional to the device periphery, with the coefficient of proportionality dependent on the shape of the metal. The parallel-plate component of the device capacitance is modulated by the applied voltage; the edge component is nearly independent of the applied voltage. Hence, the largest capacitance modulation is achieved in devices with the smallest ratio of the device periphery over the device area, which has the smallest edge effect. The measured capacitances of small round GaAs Schottky barrier diodes are in reasonable agreement with calculated results     

Impurity incorporation and the surface morphology of MOVPE grown GaAs

The impact of impurity incorporation on the development of the surface morphology of GaAs epilayers, grown by metalorganic vapor phase epitaxy (MOVPE), has been systematically investigated. A variety of different doping elements, including Mg, Zn, C, Si, O, and Se, were used to study the interaction between the impurity atoms and GaAs surface. Impurity atoms with smaller atomic weight, belonging to group II and VI, have a larger influence on the surface morphology than the other dopants. Different chemical sources for carbon doping were also used to explore the effect of surface growth chemistry on the formation of surface features. The epilayer surface morphology was affected by the combination of several physical and chemical factors. Factorsinfluencing the impact of an impurity on the growth front evolution are presented based on the interaction between the impurity atoms and the surface step structures.     

A D-band frequency doubler with GaAs Schottky varistor diodes

A D-band hybrid frequency doubler is developed with varistor diodes. The multiplier circuit substrate is RT/duroid 5880 with a thickness of 0.127 mm. In the circuit, the improved waveguide to unilateral finline transition is implemented with lower transition loss by cutting off high-order modes, and the reliability of the mounted circuit is enhanced with increased mounting groove depth. The D-band doubler exhibits the highest efficiency of 2% at 150.2 GHz; the typical efficiency is 1.9% from 150 to 150.5 GHz. The experimental and simulated results are in good agreement.     

Schottky diodes for analogue phase shifters in GaAs MMICs

A simple Schottky diode structure, which is easily implemented in a foundry gallium arsenide (GaAs) process, is described. This structure occupies very much less area than the usual technique of realising Schottky diodes, using standard FET structures. Two variations of the diode have been characterized and modeled using a standard equivalent circuit. This has been used to design a simple analogue phase shifter based on a loaded-line configuration. The phase shifter was manufactured using a standard foundry process and has shown excellent results in terms of phase shift linearity with tuning voltage, combined with low insertion loss, over the range 2-8 GHz     

New photoluminescence lines in Vanadium doped GaAs grown by MOVPE

We examined the electrical and optical properties of vanadium-doped GaAs grown by metalorganic vapour phase epitaxy using vanadium tetrachloride (VCl₄) as a novel dopant source. Samples with various vanadium incorporations were investigated. All samples were n type. The electron concentration dependence on the VCl₄ flow rate was established. At 15 K, by comparison with undoped layers grown in the same conditions, photoluminescence spectra of V-doped exhibited three new emission bands: at 1.41, 1 and 0.72 eV. The 1 and 0.72 eV band emissions were attributed to V²⁺ and V³⁺ intracenter emission, while the 1.41 eV band was suggested to be a donor-bound transition. The identity of the donor is tentatively attributed to a donor complex that associates vanadium to an arsenic vacancy. From Hall effect as function of temperature, the donor ionisation energy was estimated to be about 102±5 meV.     

Annealing effect in Si-doped GaAs and AlGaAs layers grown by MBE

The effect of annealing on Si-doped GaAs and Al0·3Ga0·7As layers grown by MBE has been studied. In the heavily doped samples, the donor concentration decreased considerably and the broad luminescence characteristic of the SA centre reported in bulk n-GaAs appeared. The results suggest evidence that annealing converts some of the Si donors into complexes like the SA centre, which does not act as a donor.     

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     

Investigation of GaAs Schottky barrier diodes in the THz range

The properties of GaAs Schottky barrier diodes as video detectors and mixing elements were investigated in the frequency range from 0.8–2.5 THz. For the most sensitive diode, the video responsivity and system noise temperature were measured as a function of incident laser power. The highest video responsivity was 2,000 V/W at 214μm and 60 V/W at 118μm. For five diodes differing in doping, capacitance, series resistance and anode diameter, the system noise temperature was measured at 214μm and 118μm. The best single sideband (SSB) values are 12,300 K and 24,200 K at 214μm and 118μm, respectively. The system noise temperature versus frequency is given over the range from 0.5–3 THz for two specific diodes demonstrating that the sharpness of the I–V characteristics is only of secondary importance for mixer perfomance at such high frequencies.