P. K. Basu

Bio: P. K. Basu is an academic researcher. The author has contributed to research in topics: Superlattice & Semiconductor. The author has an hindex of 1, co-authored 1 publications receiving 277 citations.

Theory of optical processes in semiconductors : bulk and microstructures

Abstract: 1 INTRODUCTION 2 CLASSICAL THEORY OF OPTICAL PROCESSES 3 PHOTONS 4 ELECTRON BAND STRUCTURE AND ITS MODIFICATIONS 5 INTERBAND AND IMPURITY ABSORPTIONS 6 EXCITONIC ABSORPTION 7 ABSORPTION AND REFRACTION IN AN ELECTRIC FIELD 8 INTERBAND MAGNETO-OPTICAL EFFECTS 9 FREE CARRIER PROCESSES 10 RECOMBINATION PROCESSES 11 INTRODUCTION TO TWO-DIMENSIONAL SYSTEMS 12 OPTICAL PROCESSES IN QUANTUM WELLS 13 EXCITONS AND IMPURITIES IN QUANTUM WELLS 14 OPTICAL PROCESSES IN QUANTUM WIRES AND DOTS 15 SUPERLATTICES 16 STRAINED LAYERS 17 EFFECTS OF ELECTRIC FIELD ON LOW DIMENSIONAL SYSTEMS

(Photo)electrochemical Methods for the Determination of the Band Edge Positions of TiO2-Based Nanomaterials

Abstract: TiO2-based nanomaterials play currently a major role in the development of novel photochemical systems and devices. One of the key parameters determining the photoactivity of TiO2-based materials is the position of the band edges. Although its knowledge is an important prerequisite for understanding and optimizing the performance of photochemical systems, it has been often rather neglected in recent research, particularly in the field of heterogeneous photocatalysis. This paper provides a concise account of main methods for the determination of the position of the band edges, particularly those suitable for measurements on nanostructured materials. In the first part, a survey of key photophysical and photochemical concepts necessary for understanding the energetics at the semiconductor/solution interface is provided. This is followed by a detailed discussion of several electrochemical, photoelectrochemical, and spectroelectrochemical methods that can be applied for the determination of band edge positions in compact and nanocrystalline thin films, as well as in nanocrystalline powders.

Introduction to Optical Quantum Information Processing

Abstract: Quantum information processing offers fundamental improvements over classical information processing, such as computing power, secure communication, and high-precision measurements. However, the best way to create practical devices is not yet known. This textbook describes the techniques that are likely to be used in implementing optical quantum information processors. After developing the fundamental concepts in quantum optics and quantum information theory, the book shows how optical systems can be used to build quantum computers according to the most recent ideas. It discusses implementations based on single photons and linear optics, optically controlled atoms and solid-state systems, atomic ensembles, and optical continuous variables. This book is ideal for graduate students beginning research in optical quantum information processing. It presents the most important techniques of the field using worked examples and over 120 exercises.

Laser cooling of a semiconductor by 40 kelvin

Abstract: Net laser cooling from 290 kelvin to about 250 kelvin is achieved in semiconductor cadmium sulphide ‘nanobelts’ and attributed to strong coupling between excitons and longitudinal optical phonons. Laser cooling of solids, or optical refrigeration, is attractive as a route to compact, cryogen-free and vibration-free refrigeration devices. Laser cooling, based on removing heat due to blue-shifted emission, has been reported previously in rare-earth-metal-doped glasses and crystals. Now Jun Zhang et al. demonstrate a substantial net laser cooling of a semiconductor CdS nanobelt — by about 40 K from 290 K pumped by a 514-nm laser. This achievement opens up a route to optical refrigeration based on semiconductors, where the mechanisms involve excitonic rather than atomic resonances. Laser cooling media based on II–VI semiconductors are potentially highly efficient, capable of achieving extremely low temperatures and readily integrated into optoelectronic devices. Optical irradiation accompanied by spontaneous anti-Stokes emission can lead to cooling of matter, in a phenomenon known as laser cooling, or optical refrigeration, which was proposed by Pringsheim in 19291. In gaseous matter, an extremely low temperature can be obtained in diluted atomic gases by Doppler cooling2, and laser cooling of ultradense gas has been demonstrated by collisional redistribution of radiation3. In solid-state materials, laser cooling is achieved by the annihilation of phonons, which are quanta of lattice vibrations, during anti-Stokes luminescence. Since the first experimental demonstration in glasses doped with rare-earth metals4, considerable progress has been made, particularly in ytterbium-doped glasses or crystals: recently a record was set of cooling to about 110 kelvin from the ambient temperature, surpassing the thermoelectric Peltier cooler5,6. It would be interesting to realize laser cooling in semiconductors, in which excitonic resonances dominate7,8,9, rather than in systems doped with rare-earth metals, where atomic resonances dominate. However, so far no net cooling in semiconductors has been achieved despite much experimental10,11,12 and theoretical7,8,9,13,14 work, mainly on group-III–V gallium arsenide quantum wells. Here we report a net cooling by about 40 kelvin in a semiconductor using group-II–VI cadmium sulphide nanoribbons, or nanobelts, starting from 290 kelvin. We use a pump laser with a wavelength of 514 nanometres, and obtain an estimated cooling efficiency of about 1.3 per cent and an estimated cooling power of 180 microwatts. At 100 kelvin, 532-nm pumping leads to a net cooling of about 15 kelvin with a cooling efficiency of about 2.0 per cent. We attribute the net laser cooling in cadmium sulphide nanobelts to strong coupling between excitons and longitudinal optical phonons (LOPs), which allows the resonant annihilation of multiple LOPs in luminescence up-conversion processes, high external quantum efficiency and negligible background absorption. Our findings suggest that, alternatively, group-II–VI semiconductors with strong exciton–LOP coupling could be harnessed to achieve laser cooling and open the way to optical refrigeration based on semiconductors.

Can laser light cool semiconductors

Abstract: Laser cooling in semiconductors is theoretically investigated including arbitrary external efficiency and photon recycling. Experimental conditions needed to attain net cooling in GaAs are derived.

Optical band gap and the Burstein–Moss effect in iodine doped PbTe using diffuse reflectance infrared Fourier transform spectroscopy

Abstract: Optical absorption edge measurements are performed on I doped PbTe using diffuse reflectance infrared Fourier transform spectroscopy. The Burstein-Moss shift, an increase in the absorption edge (optical band gap) with increasing doping level, is explored. The optical gap increases on the order of 0.1eV for doping levels ranging from 3◊10 18 to 2◊10 20 cm 3 , relevant doping levels for good thermoelectric materials. Chemical potential is estimated from transport measurements—specifically, Hall effect and Seebeck coefficient—using a single band Kane model. In heavily doped semiconductors, it is well-known that the band gap shrinks with increasing doping level. This effect, known as band gap renormalization, is fit here using an n 1/3 scaling law which reflects an electron-electron exchange interaction. The renormalization effect in these samples is shown to be more than 0.1eV, on the same order of magnitude as the band gap itself. Existing models do not explain such large relative changes in band gap and are not entirely self-consistent. An improved theory for the renormalization in narrow gap semiconductors is required.