V. R. Balakrishnan

Inverse temperature dependence of reverse gate leakage current in AlGaN/GaN HEMT

The experimentally observed inverse temperature dependence of the reverse gate leakage current in AlGaN/GaN HEMT is explained using a virtual gate trap-assisted tunneling model. The virtual gate is formed due to the capture of electrons by surface states in the vicinity of actual gate. The increase and decrease in the length of the virtual gate with temperature due to trap kinetics are used to explain this unusual effect. The simulation results have been validated experimentally.

Effect of field dependent trap occupancy on organic thin film transistor characteristics

A model to calculate the current voltage characteristics of organic thin film transistors is presented. The model takes into account the influence of high electric field on trap occupancy. The case of the traps at a single energy level is considered in detail. Relevant equations are solved numerically using an iteration method. The field dependent trap occupancy model is found to change free surface charge Qsf and drain saturation current Id significantly. The model is compared with the experimental data published by two different groups. There is good agreement between experimental data and our model.

Interlayer formation due to group V-hydride stabilization during interruptions of MOVPE growth of InGaP

The effect of indium and arsenic carry-over and of arsenic–phosphorus exchange on unintentional interlayer formation due to prolonged stabilization under arsine or phosphine during InGaP growth interruptions in metalorganic vapour phase epitaxy (MOVPE) at 580 °C is investigated. Photoluminescence, x-ray diffraction, secondary ion mass spectrometry, transmission electron microscopy and capacitance–voltage (C–V) depth profiling of the electron concentration are used to detect and to characterize possible unintentionally formed interlayers. The C–V measurements show that purging with PH3 mainly enhances the degree of ordering of an interlayer region due to a P-rich reconstruction of the InGaP surface during the growth interruption. The interlayer stress and band offset are too small to be detected by x-ray diffraction or photoluminescence. In contrast, purging with AsH3 during InGaP growth interruption leads to strong arsenic incorporation, but does not lead to any change in the In concentration. The As-rich interlayer gives rise to additional photoluminescence peaks and compressive strain. The relatively large interlayer thickness detected by C–V and SIMS measurements of up to 20 nm indicates that arsenic accumulated during the prolonged growth interruptions carries over into the InGaP layer grown after the interruption. It is shown that the chosen growth conditions suppress the In carry-over, but As carry-over occurs additionally to the As–P exchange.

Eriocaulon govindiana sp. nov. (Eriocaulaceae), from southern Western Ghats, Kerala, India

A new species, Eriocaulon govindiana Sunil & Ratheesh, from marshy areas in the Wayanad wildlife Sanctuary, Kerala, India, is described and illustrated. It is morphologically most similar to E. nepalense but differs mainly in having well developed root stock, rounded and involute leaf apex, lobed limb of sheath, and usually a single hoary male petal. Information on habitat, distribution, phenology, and conservation status are provided.