Solid State Physics Laboratory

About: Solid State Physics Laboratory is a facility organization based out in Delhi, India. It is known for research contribution in the topics: Quantum dot & Dielectric. The organization has 1754 authors who have published 2597 publications receiving 50601 citations.

Ohmic contacts to pseudomorphic HEMTs with low contact resistance due to enhanced Ge penetration through AlGaAs layers

Abstract: AuGe/Ni ohmic contacts are used as source and drain electrodes of pseudomorphic HEMTs (pHEMTs). High alloying temperatures are generally believed to be necessary to enhance penetration of the alloy materials through the AlGaAs layers in order to establish a very low resistance path for the source–drain currents to access the two-dimensional electron gas (2DEG) layer. Here we have performed alloying experiments in the temperature range of 390–450 °C, and the contact resistance was determined using transfer length method measurements. Germanium diffusion was studied using backside secondary ion mass spectrometry. During our study, we have observed that doping of the channel by germanium is possible even at lower temperatures. But alloying at lower temperatures does not appreciably enhance the concentration throughout the different device layers below the contact pads. Hence, unlike MESFET alloying, higher alloying temperatures are essential for increasing the doping concentration so as to reduce the contact resistance and overcome the resistance of the AlGaAs layers.

A sub-circuit model of a microbolometer IR detector and its experimental validation

Abstract: In this paper, we present a generic circuit model of microbolometer Infrared detector that can be used to simulate the electrical and thermal performance of microbolometers using SPICE like circuit simulator. Using this model, we have studied the effects of various parameters on the microbolometer performance by simulations in PSPICE for its verification. We have validated the model with the performance of our titanium microbolometers being developed at our laboratory. We have tuned the model parameters for these microbolometers and have shown that the simulated performance agrees with the measured performance reasonably well with the variety of measurement condition. The validated model has been used to fine tune the design of our titanium microbolometers as it allows us to monitor some internal parameters also that are not easy to measure in practical devices, like instantaneous temperature of microbolometer for a varying IR intensity falling on it. The proposed model is generic and therefore, using similar procedure it may be used for other types of microbolometers also like amorphous-Si based, vanadium oxide based etc., once it is validated for that.

A nanoporous thin-film miniature interdigitated capacitive impedance sensor for measuring humidity

Abstract: This paper presents a development of a low-cost miniature humidity sensor with an interdigitated aluminium electrode connected in parallel on quartz substrate. Interdigitated capacitive device has been fabricated using the photolithography method. The aluminium electrode was covered with sensitive film of a nanoporous thin film of γ-Al2O3 made from novel sol–gel technique. Nanostructured thin film offers very high surface to volume ratio with distribution of micro pores for moisture detection. Pore morphologies of the film have been studied by field emission electron microscope and X-ray diffraction methods. Impedance measurement of the miniature capacitive humidity sensor toward relative humidity was investigated at room temperature by Agilent 4294A impedance analyzer (Agilent, Santa Clara, CA, USA). The device exhibits short response and recovery times and good repeatability.

Analytic approach to the a.c. conductance method for rapid characterization of interface states in MOS structures

Abstract: Nicollian and Goetzberger's well known integral expression for the equivalent parallel conductance due to interface states G p / ω has been given a simple analytical representation which is valid under the condition that interface potential fluctuation parameter σ > 1.5. Previous methods of conductance analysis based upon numerical and/or graphical construction are provided with alternative analytic relations. The earlier parametric numerical relations like ξ p , f w , f D and ln ( ξ + / ξ − ) vs σ are described very well by analytic expressions in this paper. A new relation is presented to determine interface state time constant from the width of conductance peak. A new method is presented to determine dependence of σ on interface band bending from G p / ω vs bias measurements at just two frequencies. The expedient method of Nicollian, Goetzberger and Lopez utilises the same two curves to determine distribution of interface state density N ss and capture cross section σ p across the band gap. Therefore using the present new method for σ determination and other analytical relations for N ss and σ p determination, the expediency of their method is greatly enhanced. Complete conductance analysis for rapid characterization of the interface is shown to become now a simple straight forward affair, and the amount of data required is also substantially reduced.