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.     

High-power 11 GHz GaAs hi-lo Impatt diodes with titanium Schottky barriers

Schottky-barrier hi-lo GaAs Impatt diodes with Ti-Pt-Au contacts have been fabricated for the 10.7?11.7 GHz band. At 180°C junction temperature rise the diodes have produced over 5 W of output power and up to 24% efficiency from an 11 GHz oscillator. Initial life tests show potential for high reliability.     

Simulation of GaAs IMPATT diodes including energy and velocity transport equations

Simulations have been performed of GaAs hybrid double-drift IMPATT diodes at 60 and 94 GHz using a transport model which includes equations for the average per-carrier velocity and energy. These equations are obtained from the second and third velocity moments of the Boltzmann transport equations, respectively. The relaxation-time formulation is used to characterize the collision terms. Simulations were also carried out for the same structures using the standard drift-diffusion transport model. It was found that inclusion of the energy-velocity equations significantly modifies the predicted carrier transport behavior and results in somewhat better RF performance under large-signal conditions than that predicted by the drift-diffusion simulation.     

Electron transport in avalanching GaAs diodes

Magnetoresistance measurements on avalanching GaAs diodes lead to an estimate of 1.6 × 10^-15sec for the scattering time of avalanching electrons at 300K. This is consistent with the time recently calculated by Monte Carlo techniques. It confirms that impact ionization by electrons in GaAs is initiated by carriers that make several collisions in the process rather than by ballistic carriers which impact ionize without any interaction with phonons.     

Delayed secondary avalanche effects in millimeter wave GaAs IMPATT diodes

A simulation of the large signal operation of GaAs millimeter wave IMPATTs shows that a high peak current density of electrons (often in excess of 25KA/cm²) will lead to a delayed secondary avalanche (DSA) in the drift zone. These DSA effects have been simulated and correlated with experimental observations and are a determining factor in achieving high power and high efficiency in GaAs IMPATTs at 40 GHz and above.     

High field transport in GaAs,InP and InAs

Calculations of the steady state and transient electron drift velocities and impact ionization rate are presented for GaAs, InP and InAs based on a Monte Carlo simulation using a realistic band structure derived from an empirical pseudopotential. The impact ionization results are obtained using collision broadening of the initial state and are found to fit the experimental data well through a wide range of applied fields. In InP the impact ionization rate is much lower than in GaAs and no appreciable anisotropy has been observed. This is due in part to the larger density of states in InP and the corresponding higher electron-phonon scattering rate. The transient drift velocities are calculated under the condition of high energy injection. The results for InP show that higher velocities can be obtained over 1000–1500 Å device lengths for a much larger range of launching energies and applied electric fields than in GaAs. For the case of InAs, due to the large impact ionization rate, high drift velocities can be obtained since the ionization acts to limit the transfer of electrons to the satellite minima. In the absence of impact ionization, the electrons show the usual runaway effect and transfer readily occurs, thus lowering the drift velocity substantially.     

A millimeter wave large-signal model of GaAs planar Schottky varactor diodes

A millimeter wave large-signal model of GaAs planar Schottky varactor diodes based on a physical analysis is presented.The model consists of nonlinear resistances and capacitances of the junction region and external parasitic parameters.By analyzing the characteristics of the diode under reverse and forward bias,an extraction procedure of all of the parameters is addressed.To validate the newly proposed model,the PSVDs were fabricated based on a planar process and were measured using an automatic network analyzer.Measurement shows that the model exactly represents the behavior of GaAs PSVDs under a wide bias condition from -10 to 0.6 V and for frequencies up to 40 GHz.     

一种新型的砷化镓平面肖特基变容管大信号模型

A millimeter wave large-signal model of GaAs planar Schottky varactor diodes based on a physical analysis is presented.The model consists of nonlinear resistances and capacitances of the junction region and external parasitic parameters.By analyzing the characteristics of the diode under reverse and forward bias,an extraction procedure of all of the parameters is addressed.To validate the newly proposed model,the PSVDs were fabricated based on a planar process and were measured using an automatic network...     

Comparative studies of Si,GaAs, and InP millimeter-wave IMPATT diodes

High frequency limitations of Si, GaAs and InP IMPATT are investigated by concentrating on the effects of transient carrier transport and generation. A large-signal microscopic computer simulation is used to study the operating mechanisms in the 90, 140 and 220 GHz atmospheric windows. Inertial effects which can enhance or degrade the performance are identified first. The frequency and signal level dependence is then discussed in terms of intrinsic properties of materials.     

Effects of transient carrier transport in millimeter-wave GaAs diodes

Effects of transient carrier transport on the performance of millimeter-wave GaAs diodes are investigated using results obtained from a Monte Carlo simulation of electron transport. Transit-time devices (such as IMPATT's and TUNNETT's) are discussed first. Mechanisms by which transient effects in the drifting charge pulse may enhance or degrade performance are identified and discussed. Attention is then focused on electron transport in the undepleted epitaxial material which will be present in mixer and varactor diodes and may be present in transit-time diodes. The frequency and signal-level dependence of the conductance of such material is calculated and the implications for device performance are discussed.     

Simulation of carrier transport and nonlinearities in quantum-welllaser diodes

The two-dimensional (2-D) quantum-well (QW) laser diode simulator Minilase-II is presented in detail. This simulator contains a complete treatment of carrier dynamics including bulk transport, quantum carrier capture, spectral hole burning, and quantum carrier heating. The models used in the simulator and their connectivity are first presented. Then the simulator is used to demonstrate the effects of various nonlinear processes occurring in QW lasers. Finally, modulation responses produced by Minilase-II are compared directly with experimental data, showing good quantitative agreement     

Capacitance-Voltage characteristics of metal-insulator-semiconductor diodes with S passivation and Si interface control layers on GaAs and InP

GaAs and InP surfaces have been prepared by gas-phase and liquid-phase polysulfide passivation techniques followed by the deposition of Si interface control layers (ICLs) by e-beam evaporation. For GaAs surfaces, the performance of an ICL consisting of 1.5 nm Si on top of 0.5 nm of Ge has also been evaluated. Metal-insulator-semiconductor diodes with aluminum top electrodes were fabricated on these surfaces using silicon nitride deposited by a remote plasma-enhanced chemical vapor technique or silicon dioxide deposited by a conventional direct plasma-enhanced chemical vapor deposition technique. The quality of the interfaces was analyzed by capacitance-voltage (C-V) measurements and the interface state densities D_it were deduced from the C-V data using the high-low method. Values as low as 1.5 × 10¹² eV⁻¹cm⁻² were obtained for polysulfide-passivated GaAs surfaces with a Ge-Si or Si ICL, the lowest ever demonstrated using the high-low method for an ex-situ technique not involving GaAs epitaxy. For InP, the Si ICL does not reduce D_it below that of 2 × 10¹² eV⁻¹ cm ⁻² that was obtained for the polysulfide passivated surface. The Si ICL produces an interface that degrades more slowly on exposure to air for both GaAs and InP.     

Diffusion-profile measurement in InP with Schottky diodes

Measurements of the doping profile resulting from the diffusion of Cd into lowly-doped n-type InP are reported. The measurements were taken with Au Schottky contacts. In order to probe the doping profile in its entirety with the limited resolution depth of the Schottky diodes, thin layers of the diffused samples were removed by chemical etching in a well-controlled fashion. The etching procedure leading to smooth crystal surfaces is described in detail. The diffusion profile of Cd is characterized by a flat portion in the low 10¹⁸ cm^?3 extending to a sharp gradient coinciding with the shallow diffusion front detectable by cleaving and stain etching. Between the shallow and second diffusion front very low p-type doping is found whereas beyond the second diffusion front the n-type conductivity of the substrate is attained. Thus Cd leads to a p⁺pn transition in n^?-InP.     

Diffusion of transition elements in GaAs and InP

A technique is presented for studying the diffusion of iron and chromium in GaAs and InP at temperatures down to 600°C. The technique is reproducible, and results are presented which show that in all four cases very fast diffusion occurs.     

Modeling of steady-state optical phenomena in transistors and diodes

A lumped model is derived for photodiodes and phototransistors from which steady-state spectral properties, such as quantum efficiency, can be determined. The model is derived in a manner such that its utility extends to regions of any length ω that is, there is noomega/Lll1restriction, whereLrepresents the minority-carrier diffusion length in the region. The validity of the resulting model is demonstrated by showing that the lumped model predicts the empirically measured quantum efficiency of planar photodiodes to within 10 percent.     

Properties of GaAs alloy diodes

GaAs p⁺n alloy diodes have been developed which look attractive as varactors and high speed switches. The forward current in these diodes, which varies with voltage as exp(q V/nkT) where n is nearly one, is neither a simple diffusion current nor due to recombination in the space charge region. It can, however, be explained if one assumes that the alloyed junction is a metal-semiconductor (Schottky) barrier with a metal-semiconductor work function of 0·95 V, or if one assumes that in the alloyed region the band gap of the GaAs has been reduced to less than 1·0 V. The absolute value of the current, its temperature dependence, as well as its voltage dependence can be explained by either of these two models. Since in both these models the current is injected from the n-type base region, the lack of injection luminescence and the extremely short switching times can also be explained. Because there is no direct evidence for the reduction in band gap, the Schottky barrier model seems the more likely explanation. While these diodes may be attractive, the presence of this type of forward currents in GaAs transistors and GaAs tunnel diodes would be deleterious and may explain experimental results in these devices.     

MeV energy sulfur implantation in GaAs and InP

Room temperature and elevated temperature sulfur implants were performed into semi-insulating GaAs and InP at variable energies and fluences. The implantations were performed in the energy range 1–16 MeV. Range statistics of sulfur in InP and GaAs were calculated from the secondary ion mass spectrometry atomic concentration depth profiles and were compared with TRIM92 values. Slight in-diffusion of sulfur was observed in both InP and GaAs at higher annealing temperatures for room temperature implants. Little or no redistribution of sulfur was observed for elevated temperature implants. Elevated temperature implants showed higher activations and higher mobilities compared to room temperature implants in both GaAs and InP after annealing. Higher peak electron concentrations were observed in sulfur-implanted InP (n ≈ 1 × 10¹⁹ cm⁻³) compared to GaAs (n ≈ 2 × 10¹⁸ cm⁻³). The doping profile for a buried n⁺ layer (n ≈ 3.5 × 10¹⁸ cm⁻³) of a positive-intrinsic-negative diode in GaAs was produced by using Si/S coimplantation.     

Bulk unipolar diodes in MBE GaAs

Bulk unipolar (camel) diodes in GaAs have been made using thin, buried p+ layers doped with beryllium and grown by MBE. Barrier heights in the range 0.55 eV to 0.94 eV have been obtained by varying the p+-layer thickness. In all cases the ideality factors of the diodes were less than 1.5.     

Impedance and switching of GaAs p-i-n diodes

The impedance of GaAs p-i-n diodes under forward bias is modeled using the two-dimensional simulation program PISCES. A parallel equivalent circuit gives almost constant resistance and capacitance over a wide range of frequencies. The intrinsic turn-off switching time of the diode, neglecting contact resistance, is determined by the sweep out time of the carriers, not by the carrier lifetime, unless this is very short. The diode current is recombination dominated at low forward bias. At higher applied voltages, this current becomes diffusion dominated if not masked by high injection conditions     

Comparison of GaAs MESFET and GaAs p-i-n diodes as switch elements

The Kurokawa-Schlosser quality factor Q̂ is used to compare the GaAs MESFET switch with the GaAs p-i-n diode switch. The MESFET device parameters are governed by the power handling capability and the specified pinchoff voltage, and the switch Q̂ is calculated from an approximate expression. The GaAs p-i-n has been characterized using a simple diode model which is derived from detailed simulations. The comparison for typical devices shows that the GaAs pin has the higher Q̂ and therefore should have improved characteristics as a switch in terms of insertion loss and isolation.