High efficiency pulsed GaAs Read impatt diodes

GaAs Read impatt diodes have been developed for pulsed operation in X and Ku bands. Conversion efficiencies of 32% and 29% have been measured for p+n+n?n+ (high-low) doping profiles grown by liquid phase and vapour phase epitaxy, respectively. Peak powers of 30 W in X band and 20 W in Ku band have been obtained with single mesas on gold plated heatsinks. Multiple mesas in parallel and diamond heatsinking were employed to improve thermal resistance. Microwave circuit and chip level power combining techniques were also investigated and greater than 90% combining efficiency was achieved on the chip level.     

GaAs planar Gunn diodes for DC-biased operation

The difficulty in obtaining CW oscillations in GaAs planar Gunn diodes has been found to be due to distortion of the field distribution by a field-enhanced trapping effect. A tapered active region is proposed to compensate for the effect due to the trapping. By adopting the geometry, coherent CW Gunn oscillations have been obtained successfully with reasonable reproducibility.     

Conduction current injection delay in Read GaAs IMPATT diodes

We find experimentally that, for GaAs Read avalanche diodes, the optimal drift region width is not simply inversely proportional to optimum frequency. This finding can be understood by noting that the injection phase of the avalanche current into the drift region is not 90° with respect to the voltage maximum, but varies as a function of frequency. The experimental observations are in reasonable agreement with solutions of the Read equation which include the reverse junction saturation current. The theoretical fit to the data is relatively insensitive to the avalanche intrinsic response time, and thus we cannot make an independent determination of its value at present.     

Status of the GaAs metal—oxide—semiconductor technology

A review of recent and current work on GaAs insulated-gate technology is presented. First, various techniques for the formation of heteromorphic and homomorphic dielectrics are outlined and some important aspects of properties of these dielectrics are reviewed. Second, MOSFET structures, fabrication procedures, and microwave performance are described. Third, the application of GaAs MOSFET's to digital integrated circuits is summarized.     

All-binary AlAs—GaAs laser diode

Thin layers of AlAs and GaAs, grown by molecular beam epitaxy (MBE), are used to simulate the properties of AlxGa1-xAs. These AlAs-GaAs superlattices (SL's) are used as cladding layers (instead of AlxGa1-xAs) in heterostructure lasers capable of room-temperature operation. It is thus possible to obtain laser diodes which are composed only of the binary compounds GaAs and AlAs. The all-binary lasers are compared to conventional AlxGa1-xAs-GaAs double-heterostructure (DH) lasers grown and fabricated under similar conditions.     

Monolithic matrix-addressable AlGaAs—GaAs array

Planar monolithic matrix-addressable visible LED arrays were fabricated from the AlGaAs-GaAs material system using proton bombardment for pixel-to-pixel electrical isolation. Computer simulation was used to model the current distribution in the device in order to determine the uniformity of brightness across the emitting surface. A 5 × 7 element visible LED display was demonstrated using an ASCII character generator.     

A new concept for high-efficiency operation of high-low-type GaAs IMPATT diodes

A new operation mode, the "surfing mode," is proposed as an explanation for the high-efficiency operation of high-low-type GaAs IMPATT diodes. This mode is characterized by the concept that the avalanche charge pulse drifts synchronously with the movement of the front edge of the depletion layer at a velocity higher than the saturation velocity. The design chart of high-low-type GaAs IMPATT diodes is determined on the basis of the concept of the "surfing mode." The high-low-type GaAs IMPATT diodes designed using this chart exhibited output powers of 15.3 W (Delta T_{j}= 210°C) at 6.1 GHz with 25-percent efficiency.     

Current-tuned GaAs Schottky-barrier Impatt diodes for 60?96 GHz operation

Oscillation of GaAs single-drift Schottky-barrier Impatt diodes mounted in a full-height IEC-R740 waveguide (3.1 × 1.55 mm2) has been observed between 60 and 96 GHz in pulsed operation. By bias-current tuning, a range of up to 19 GHz was covered with a single diode.     

Low-frequency noise in Cr—SiO2—N-Si tunnel diodes

Low-frequency noise of Cr-SiO2-n-Si tunnel diodes with about 30-Å-thick oxides is investigated as function of bias, frequency, and temperature. Measurements of1/fnoise are explained by a theory employing the two step tunneling model of Sah. Electrons from the Si conduction band are trapped by states at the Si-SiO2interface and then tunnel into bound states of the oxide located close to the interface. The oxide states of density N00can be represented by a frequency dependent parallel admittance exhibiting frequency-dependent thermal noise that modulates the dc currentItunneling through the oxide barrier. This generates flicker noise at the device terminals proportional toI^{2}N_{00}and inversely proportional to frequencyfand tunneling areaA. The valueA = 5. 10-3A0, determined by fitting theoretical and experimental curves at low frequency, is only a small fraction of the gate area A0, since tunneling preferentially occurs through the thinnest parts of the oxide. The currentIalso exhibits full shot noise at high frequency and low current. Qualitative agreement between theoretical and measured noise is found over 9 decades. Measurements at low temperature show additional noise of generation-recombination centers at larger frequencies and currents.     

CW operation of GaAs planar Gunn diodes with evaporated contacts

The modification of an evaporated contact GaAs Gunn diode is reported in which geometry control is used to achieve improved terminal characteristics. The devices operate in a CW mode at a reduced terminal voltage and have excellent trigger response.     

Monolithic integration of a metal—semiconductor—metal photodiode and a GaAs preamplifier

A metal-semiconductor-metal (MSM) photodiode and a preamplifier have been monolithically integrated on a GaAs substrate by a very simple fabrication process. Measurements have shown that the constituent MSM photodiode has a sensitivity of 2.2 A/W and a -3-dB cutoff frequency of as high as 1 GHz. The present photodiode has been found to realize an extremely high photosensitivity of the monolithically integrated circuit, 26 mV/µW.     

Impedance measurement of the illuminated metal—SiO2—Si diodes

Impedance measurement of light-illuminated MIS diodes was made. It becomes clear from the results that in the inversion region conductance of the MIS structure is more sensitive to illumination than its capacitance and that negative photoconductivity appears at low frequency, which is explained by the theory of Grosvalet et al.     

Condition for no charge accumulation on a metal of a Schottky—Schottky connection in a system of Gunn devices

Possibility of the charge accumulation on a metal of a Schottky barrier, prepared for triggering a Gunn device, is pointed out and experimental evidences shown when a trigger input is fed through another series Schottky barrier of opposite polarity. A theory is developed which shows conditions for avoiding the phenomenon.     

A technique for the investigation of deep-level states in diffused p—N junction devices: Application to GaAs electroluminescent diodes

Analytical equations describing the high-frequency (1 MHz) capacitance-voltage (C-V) characteristics have been derived for diffused p-n junction diodes, including the effect of deep-level states within the bandgap. It was found that the C^-3versusVcurve becomes nonlinear when the density of the deep-level states is large. From the derivedC-Vequation the density of the deep-level states may be calculated from the slope of theC^{3}VversusC(V- V_{2})/V^{2}curve, where V2is related to the energy level of the deep states. The value of V2may be determined from the recombination current versus temperature measurements at small bias. The theory has been applied to characterize the dominant deep-level recombination centers in Zn-diffused GaAs light-emitting diodes. The measured deep levels are within 0.2 eV of the midgap energy and the density of these centers is of the order of 10¹⁶cm^-3.     

Noise characteristics of GaAs and Si IMPATT diodes for 50-GHz range operation

Direct comparison of noise behaviors between GaAs Schottky-barrier junction and Si diffused p⁺-n junction diodes operating in the 50-GHz range is reported by using the same circuitry. In the oscillator operation, the GaAs diode exhibits excess "1/f^m" noise near carrier, whereas the Si diode shows flat spectrum. Far from the carrier, and AM-DSB-NSR of -133 dB in a 100-Hz bandwidth and an FM noise measure of 27.1 dB are observed for GaAs diodes. Corresponding values obtained for Si diodes are -125 and 36.2 dB, respectively. As a reflection amplifier, minimum noise figures of 27.5 and 38 dB are achieved for the GaAs and Si devices, respectively. These results indicate that the GaAs IMPATT is superior in noise behavior to the Si diode also in the 50-GHz frequency range by about 10 dB. It is emphasized that the noise induced in the bias circuit of the IMPATT oscillator is a replica of the sideband noise of the output power and can be used as an indicator to obtain a low-noise tuning condition of the oscillator.     

Al—Ge ohmic contacts to n-type GaAs

Ohmic contacts have been fabricated to n-type GaAs with an alloy of AL-Ge which has an eutectic temperature of 424°C with 53- weight percent Germanium. The lowest contact resistance of 1.4 × 10^-6Ω.cm²was measured with a transfer length transmission line structure. The application to GaAs integrated-circuit design is demonstrated.     

C.W. operation of ion-implanted GaAs read-type IMPATT diodes

Epitaxial and ion-implantation techniques have been combined to form a high/low doping profile for GaAs Schottky-barrier Read-type IMPATT diodes. A c.w. output power of 1.1 W with 25% conversion efficiency was obtained at 11 GHz.     

Control of gate—Drain avalanche in GaAs MESFET's

The onset of gate-drain avalanche imposes an important fundamental constraint on the drain voltage swing, and hence, on the output power of GaAs FET's. In this paper we show that recognition of the role of surface depletion and proper attention to channel design can yield avalanche voltage factors of 2-3 above bulk values. The appropriate design strategy is minimization of the undepleted epitaxial charge per unit area (Qu) between gate and drain, which, in turn, dictates a gate-notch depth approximately equal to the surface zero-bias depletion depth. A simple lateral spreading model is proposed which predicts thatV_{L} sim 50Qmin{u}max{-1}, where VLis the gate-drain avalanche voltage and Quis measured in units of 10¹²electrons/cm². This prediction is supported by a large body of experimental dc and pulse data, although considerable scatter is observed which we have attributed to epi charge nonuniformities, premature avalanche at the rough edges of AI gates formed by a liftoff process, and surface charging variations associated with dielectric passivation. The observed dependence of VLon epi charge rather than on doping level, as predicted for bulk avalanche, provides convincing evidence for nonbulk two-dimensional avalanche in the thin-film (Q_{u} < 2.3) FET geometry. In thick films (Q_{u} > 2.6), on the other hand, it is found that the bulk avalanche predictions are reasonably accurate. In terms of saturated epi current Is, the bulk regime corresponds toI_{s} > 450mA/mm and the lateral spreading (thin-film) regime toI_{s} < 400mA/mm. Finally, we have found that gate-drain avalanche is the major cause of output saturation as a function of drain potential in power GaAs FET's.     

Low-frequency excess noise in metal—Silicon Schottky barrier diodes

Theoretical models for the generation-recombination noise and trapping noise in metal-semiconductor Schottky barrier diodes are developed. Low-frequency excess noise in Schottky barrier diodes is found to be dominated by the modulation of the barrier height φB caused by fluctuation in the charge state of traps or generation-recombination centers. This noise mechanism does not occur in p-n junctions. The bias and the temperature dependence of the generation-recombination noise is critically compared with the experimental data for forward diode current ranges from 3 to 300 µA and operating temperatures from -25° to 100°C. Trapping noise in Schottky barrier diodes is observed at low temperatures in diodes not intentionally doped with deep level impurities. The experimental results on trapping noise can be described by assuming that the trap states have a constant capture cross section and are uniformly distributed in space, as well as in energy. The surface potential at the diode periphery also has an important effect on the Schottky barrier diode noise. The best low-frequency noise behavior is found when the surface is at the flat-band condition. An accumulated surface is always associated with a large amount of low-frequency excess noise.     

Output properties of charge-injection devices: Part I—Read on injection

New information concerning the readout of charge-injection device (CID) arrays, used for optical detection, is obtained from the well known Kirchhoff voltage equation for surface potential. Emphasis is placed on those readout modes involving read on injection which have been found useful with infrared-sensitive CID's. The theory obtained relates surface potential, depletion depth, mobile charge in the inversion well, and voltage on the floating gate before, during, and after injection. Previous work which obtained some properties of individual gates with filled or empty inversion wells is extended to pairs of coupled gates and partially filled potential wells. Coupled gates operating in ideal mode and in charge-sharing mode, with either column injection or row injection are included. Additional properties derived are high-frequency differential capacitance, output voltage, readout efficiency and its differential analog, transient response, charge-sharing efficiency, and differential charge-sharing efficiency. Numerical computations are given for representative CID pixels on InSb.