Signal-injection triggering of X band Gunn oscillators for f.s.k. operation

Experimental results show that the threshold effects of signal-injection triggering of Gunn oscillators can be employed for binary frequency-shift-keyed regenerator operation.     

Suppression of InP substrate degradation by hydrogen plasma caused by the presence of phosphorus vapour

It is demonstrated that the degradation of InP substrates in a hydrogen plasma can be prevented by the introduction of phosphorus vapour into the reaction chamber. The results obtained, using standard surface analysis techniques and photoluminescence depth profiling, indicate that the stoichiometry of the InP surface region can be preserved and the number of P-vacancies which diffuse into the bulk drastically reduced.<>     

Experiments on heat sinking of semiconductor devices

A planar GaAs structure has been used to measure the properties of good heatsinks of c.w. devices. It is found, first, that the thermal resistance is primarily given by the thermal conductivity k of GaAs if the temperature dependence of k is included, and, secondly, that the contribution of the semiconductor-metal interface is negligible.     

XPS analysis of (100) GaAs surfaces after applying a variety of technology-etchants

XPS measurements were undertaken on differently treated (100)-GaAs surfaces using $\text{2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and 3d core level peaks of As and Ga and the 1s level peak of 0. The $\text{2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ level peaks are more sensitive to the direct surface composition while the 3d peaks reflect the more bulk-like composition. It was found that 0 is bonded to surface As atoms in NaOH + H₂O₃ etched samples, while in HCl etched samples 0 is probably bonded to defects produced by the formation of GaO bonds. Depth profiles obtained by sputtering show a depletion of both Ga and As in the surface region. The depletion of Ga, however, is much more obvious in the HCl treated samples compared to NaOH + H₂O₂ treated samples. In interpretation of depth profiles obtained by sputtering one has to be aware of sputtering artifacts demonstrated also in this paper.     

Calculation of the power capabilities of HBT amplifiers based on a new physical HBT model

A novel model for the simulation of the microwave power capabilities of HBTs is presented. The model is based on physical analytical formulation of the terminal currents as functions of the base-emitter and base-collector voltages. It takes into account the unequal thermal distribution of temperature for multifinger HBT devices, the impact ionization, tunnelling, recombination currents, etc. From the simulation of multi-finger transistor structures it can be concluded that high thermal device resistances are detrimental for power performance, because of the unequal distribution of temperature and, hence, base current in the HBT structure. In can also be concluded that the input and output reflection coefficients are insensitive to temperature variation. Finally, it has been shown theoretically and experimentally that the breakdown voltage increases slightly with increasing operating temperature. © 1996 John Wiley & Sons, Inc.     

Reliability aspects of high temperature power MOSFETs

Gate oxide reliability and thermal shock resistance of power MOSFETs for high temperature applications, have been investigated by accelerated tests and several analytical and electrical techniques. Thermal shock tests have been performed between -40°C and 200°C with subsequent electrical tests and failure analysis. Time Dependent Dielectric Breakdown (TDDB) of the gate oxide has been studied in detail by means of in-situ leakage current measurements at various voltages and temperatures.A statistical analysis of the results yields information on the underlying failure time distribution, failure mechanisms and lifetime.     

New approach to the design and the fabrication of THz Schottkybarrier diodes

GaAs Schottky barrier diodes with near-ideal electrical and noise characteristics for mixing applications in the terahertz frequency range are described. The conventional formulas describing these characteristics are valid only in a limited forward bias range, corresponding to currents much smaller than the operating currents under submillimeter mixing conditions. Therefore, generalized analytical expressions for the I-V and C-V characteristics of the metal-semiconductor junction in the full bias range are given. A new numerical diode model is presented which takes into account not only the phenomena occurring at the junction, such as current dependent recombination and drift/diffusion velocities, but also the variations of electron mobility and electron temperature in the undepleted epi-layer. A diode fabrication process based on the electrolytic pulse etching of GaAs in combination with an in situ platinum plating for the formation of the Schottky contacts is described. Schottky barrier diodes with a diameter of 1 μm fabricated by this process have already shown excellent results in a 650-GHz waveguide mixer at room temperature     

Coherent Generation and Detection of Continuous Terahertz Waves Using Two Photomixers Driven by Laser Diodes

We report on a completely coherent, tunable, continuous-wave THz system where, for the first-time, both the transmitter and receiver are log-periodic-antenna coupled LTG-GaAs based finger-photomixers. This compact room-temperature system exhibits signal-to-noise ratios (> 10³) comparable to or better than what is reported in the literature, and has potential applications in high-resolution spectroscopy and imaging. For the purpose of demonstration, we also present results of spectroscopy measurements carried out on fused silica, which are in agreement with previously published THz-TDS measurements.     

Electrical characterisation of Si3N4/SiO2 double layers on p-type 6H–SiC

MNOS, MNS and MOS devices have been fabricated on p-type 6H–SiC substrates without epitaxial layers. They have been characterised using high frequency CV, GV, and IV measurements. The high frequency CV characteristics of p-type 6H–SiC MNOS structures indicate a very similar interface quality to p-type 6H–SiC MOS devices. A lower effective fixed insulator charge Q_I is found in MNOS devices with a higher oxide thickness x_ox. An x_ox of 10 nm is effective in avoiding charge instability. The effective fixed insulator charge Q_I can be modified in the 10 nm oxide SiC MNOS devices by injecting carriers into the nitride. Similar leakage current characteristics compared to p-type 6H–SiC MNS structures have been found for p-type 6H–SiC MNOS devices, but the SiO₂/Si₃N₄ insulator current is lower, particularly for positive electric fields. At the oxide breakdown limit (−10 MV/cm), Poole–Frenkel conduction is observed in the nitride for negative electric fields due to direct tunnelling of holes into the nitride.