Testing and Characterization of Silicon Devices at Cryogenic Temperatures

Satellite and space exploration applications require electronics which are capable of operation at extremely low temperatures (T<40K). Low temperature device models are essential for the design of circuits operating in these extreme environments. To address these needs, a helium Dewar test setup has been constructed and used to evaluate several MOSFET devices, a bipolar device, and a tunneling structure. The temperature dependent performance of each has been characterized down to 20K and, in some cases, as low as 4K. Complete voltage and temperature dependent MOSFET characteristics have led to the development of a simulator which predicts device performance at cryogenic temperatures. A tunneling structure has demonstrated comparable low temperature voltage reference performance to that of a silicon germanium voltage reference circuit

Study of Novel Power Semiconductor Devices for Performance and Reliability.

Power Semiconductor Devices are crucial components in present day power electronic systems. The performance and efficiency of the devices have a direct correlation with the power system efficiency. This dissertation will examine some of the components that are commonly used in a power system, with emphasis on their performance characteristics and reliability. In recent times, there has a proliferation of charge balance devices in high voltage discrete power devices. We examine the same charge balance concept in a fast recovery diode and a MOSFET. This is crucial in the extending system performance at compact dimensions. At smaller device and system sizes, the performance trade-off between the ON and OFF states becomes all the more critical. The focus on reducing the switching losses while maintaining system reliability increases. In a conventional planar technology, the technology places a limit on the switching performance owing to the larger die sizes. Using a charge balance structure helps achieve the improved trade-off, while working towards ultimately improving system reliability, size and cost. Chapter 1 introduces the basic power system based on an inductive switching circuit, and the various components that determine its efficiency. Chapter 2 presents a novel Trench Fast Recovery Diode (FRD) structure with injection control is proposed in this dissertation. The proposed structure achieves improved carrier profile without the need for excess lifetime control. This substantially improves the device performance, especially at extreme temperatures (-40oC to 175oC). The device maintains low leakage at high temperatures, and it\u27s Qrr and Irm do not degrade as is the usual case in heavily electron radiated devices. A 1600 diode using this structure has been developed, with a low forward turn-on voltage and good reverse recovery properties. The experimental results show that the structure maintains its performance at high temperatures. In chapter 3, we develop a termination scheme for the previously mentioned diode. A major limitation on the performance of high voltage power semiconductor is the edge termination of the device. It is critical to maintain the breakdown voltage of the device without compromising the reliability of the device by controlling the surface electric field. A good termination structure is critical to the reliability of the power semiconductor device. The proposed termination uses a novel trench MOS with buried guard ring structure to completely eliminate high surface electric field in the silicon region of the termination. The termination scheme was applied towards a 1350 V fast recovery diode, and showed excellent results. It achieved 98% of parallel plane breakdown voltage, with low leakage and no shifts after High Temperature Reverse Bias testing due to mobile ion contamination from packaging mold compound. In chapter 4, we also investigate the device physics behind a superjunction MOSFET structure for improved robustness. The biggest issue with a completely charge balanced MOSFET is decreased robustness in an Unclamped Inductive Switching (UIS) Circuit. The equally charged P and N pillars result in a flat electric field profile, with the peak carrier density closer to the P-N junction at the surface. This results in an almost negligible positive dynamic Rds-on effect in the MOSFET. By changing the charge profile of the P-column, either by increasing it completely or by implementing a graded profile with the heavier P on top, we can change the field profile and shift the carrier density deeper into silicon, increasing the positive dynamic Rds-on effect. Simulation and experimental results are presented to support the theory and understanding. Chapter 5 summarizes all the theories presented and the contributions made by them in the field. It also seeks to highlight future work to be done in these areas

Bismuth Surfactant Effects for GaAsN and Beryllium Doping of GaAsN Grown by Molecular Beam Epitaxy

Bi was investigated as a possible surfactant for growth of GaAs1-xNx layers on (100) GaAs substrates by molecular beam epitaxy using an RF plasma nitrogen source. Bi extends the useable growth conditions producing smoother surfaces to a significantly higher N content than without Bi. The conductivity of Be-doped GaAsN decreased significantly with increasing N concentration. Temperature dependent Hall measurement suggests possible compensation and increased activation energy. SIMS and Raman measurements indicate that the N composition increased by introducing Be, and for low [N], Bi. The addition of Bi during growth of Be-doped GaAsN only produced semi-insulating layers. GaAs1-xNx layers and quantum dot-like structures were grown on (100) GaAs substrates by molecular beam epitaxy. The dependence of photoluminescence emission spectra on annealing temperature is consistent with literature at lower temperatures but after annealing at 750 ºC a net red-shift is consistently observed. X-ray photoelectron spectroscopy measurements indicate that for different annealing times and temperatures, the nitrogen and arsenic surface concentrations changed compared to that of as-grown samples, specifically arsenic is lost from the material. Raman measurements are consistent with the trends in photoluminescence and also suggest the loss of arsenic occurs at higher annealing temperatures in both samples capped with GaAs and uncapped samples. The real substrate temperature preliminarily estimated by pyrometer measurement was further verified and determined by RHEED pattern transition. RHEED was also employed to observe the surface reconstruction. To optimize growth conditions, surface phase diagrams of As4/Ga BEP flux vs. the real substrate temperature under fixed As4 BEP ~4.5x10-6 Torr and fixed growth rate 0.46 μm/hr (0.45ML/s) were obtained. Different aperture plates of RF-plasma nitrogen discharge tube were used. Only the one with 10 x Ø0.2mm holes is able to produce streaky RHEED patterns under some growth circumstances, and was eventually selected to lead nitrogen species through for all growths in this work. Ga flux, N flow rate, and RF power were all found to be critical factors affecting the resultant N concentrations

РАСЧЕТ СТАТИЧЕСКИХ ПАРАМЕТРОВ КРЕМНИЕВОГО ДИОДА, СОДЕРЖАЩЕГО В СИММЕТРИЧНОМ p–n-ПЕРЕХОДЕ δ-СЛОЙ ТОЧЕЧНЫХ ТРЕХЗАРЯДНЫХ ДЕФЕКТОВ

The study of semiconductor materials and devices containing a narrow layer of impurity atoms and/or intrinsic point defects of the crystal lattice is of fundamental and practical interest. The aim of the study is to calculate the electric parameters of a symmetric silicon diode, in the flat p–n-junction of which a δ-layer of point triple-charged t-defects is formed. Such a diode is called p–t–n-diode, similarly to p–i–n-diode.Each t-defect can be in one of the three charge states (−1, 0, and +1; in the units of the elementary charge). It is assumed that at room temperature all hydrogen-like acceptors in p-region and hydrogen-like donors in n-region are ionized. It was assumed that the cross-section for v-band hole capture on t-defects is greater than the cross-section for c-band electron capture on t-defects.The system of stationary nonlinear differential equations, which describe in the drift-diffusion approximation a migration of electrons and holes in semiconductors, is solved numerically. The static capacityvoltage and current-voltage characteristics of the silicon diode with nondegenerate regions of pand n-type of electrical conductivity are calculated for forward and reverse electric bias voltage.It is shown by calculation that in the p–t–n-diode containing the δ-layer of t-defects, at the forward bias a region of current density stabilization occurs. At the reverse bias the current density in such a diode is much greater than the one in a p–n-diode without t-defects. With the reverse bias the capacitance of the p–t–n-diode, in contrast to the p–n-diode, increases at first and then decreases.Научный и практический интерес представляет изучение полупроводниковых материалов и приборов с узким слоем атомов примесей и/или собственных точечных дефектов кристаллической решетки. Цель работы – рассчитать электрические параметры симметричного кремниевого диода, в плоском p–n-переходе которого сформирован δ-слой точечных трехзарядных t-дефектов. Такой диод называется p–t–n-диодом, подобно p–i–n-диоду.Каждый t-дефект может находиться в одном из трех зарядовых состояний (−1, 0, +1; в единицах элементарного заряда). Считается, что при комнатной температуре все водородоподобные акцепторы в p-области и водородоподобные доноры в n-области ионизованы. Принималось, что сечение захвата дырок v-зоны на t-дефекты больше сечения захвата электронов c-зоны на t-дефекты.Численно решена система cтационарных нелинейных дифференциальных уравнений, описывающих в дрейфово-диффузионном приближении миграцию электронов и дырок в полупроводниках. Рассчитаны статические вольт-фарадные и вольт-амперные характеристики кремниевого диода с невырожденными областями p- и n-типа электропроводности при прямом и обратном электрическом напряжении смещения.Расчетным путем показано, что в p–t–n-диоде, содержащем δ-слой t-дефектов, при прямом смещении имеется участок стабилизации плотности тока. При обратном смещении плотность тока в таком диоде много больше, чем в p–n-диоде без t-дефектов. При увеличении обратного смещения емкость p–t–n-диода, в отличие от p–n-диода, вначале увеличивается, а затем уменьшается

The Third International Symposium on Space Terahertz Technology: Symposium proceedings

Papers from the symposium are presented that are relevant to the generation, detection, and use of the terahertz spectral region for space astronomy and remote sensing of the Earth's upper atmosphere. The program included thirteen sessions covering a wide variety of topics including solid-state oscillators, power-combining techniques, mixers, harmonic multipliers, antennas and antenna arrays, submillimeter receivers, and measurement techniques

Radiation effects on silicon solar cells Final report, Dec. 1, 1961 - Dec. 31, 1962

Displacement defects in silicon solar cells by high energy electron irradiation using electron spin resonance, galvanometric, excess carrier lifetime, and infrared absorption measurement

Some electrical and optical properties of cadmium sulphide

Imperial Users onl

Solar energy conversion through the interaction of plasmons with tunnel junctions. Part A: Solar cell analysis. Part B: Photoconductor analysis

A solar cell utilizing guided optical waves and tunnel junctions was analyzed to determine its feasibility. From this analysis, it appears that the limits imposed upon conventional multiple cell systems also limit this solar cell. Due to this limitation, it appears that the relative simplicity of the conventional multiple cell systems over the solar cell make the conventional multiple cell systems the more promising candidate for improvement. It was discovered that some superlattice structures studied could be incorporated into an infrared photodetector. This photoconductor appears to be promising as a high speed, sensitive (high D sup star sub BLIP) detector in the wavelength range from 15 to over 100 micrometers

InAs/Ga(In)Sb superlattice based infrared detectors using nBn design

Infrared detectors in the mid-wave infrared (MWIR) (3-5μm) and long-wave infrared (LWIR) (8-12μm) have many applications in military, industrial and medical fields. The state-of-the-art photodetectors based on Hg1-xCdxTe (MCT) have large signal over noise ratio and their bandgap can be tuned to span 1-32 μm wavelength range. However, large tunneling and Auger dark currents due to low electron effective mass in MCT detectors require operation at cryogenic temperatures (77-100 K). The cooling requirement limits the lifetime, adds weight and expense and increases the power consumption of the infrared system. There is a concerted effort to develop photonic detectors operating at higher temperatures. InAs/GaSb strained layer superlattice (SLS) photodectors are now considered as a promising technology for both MWIR and LWIR wavelength ranges. The bandgap of the SLS can be adjusted by controlling the thickness of the constituent InAs and GaSb layers during the growth process. InAs/GaSb SLS can also span the 3-30 μm wavelength range. Moreover, the large splitting of the energy levels of the different valence subbands in SLS contribute to the suppression of Auger recombination. The recently proposed nBn heterostructure design has demonstrated a 100 K increase in background-limited infrared photodetection (BLIP) for InAs-based device, by decreasing Shockley-Read-Hall generation currents and by suppressing surface currents using specific processing. This work is focused on combining the nBn detector design with InAs/GaSb superlattice material utilizing an AlGaSb barrier layer to improve detector performance and to increase the operating temperature of Focal Plane Arrays. This thesis covers three topics: Optical and electrical characteristics of single pixel devices in both the MWIR and LWIR, the reduction of surface leakage currents by using a shallow isolation etch for definition of the top contact mesa and comparison between nBn detector and PIN LWIR detectors

Bolometers

Infrared Detectors and technologies are very important for a wide range of applications, not only for Military but also for various civilian applications. Comparatively fast bolometers can provide large quantities of low cost devices opening up a new era in infrared technologies. This book deals with various aspects of bolometer developments. It covers bolometer material aspects, different types of bolometers, performance limitations, applications and future trends. The chapters in this book will be useful for senior researchers as well as beginning graduate students