Shambhu Nath Biswas

Effective electron mass in narrow-band-gap IR materials under different physical conditions

In this paper we have studied the effective electron mass in infrared materials under various quantiations of band states (e.g. under magnetic quantization, cross—field configuration, size quanti— zation, quantum wells under cross—field configuration, quantum wires electric field aided quantum wires, magnetic field aided QWs, cross— field configuration of QWs, QWVvs and electric field aided QWWs 4Luv eleetron energy spe ctra in the re spe ctive ease S. We have also forniu— 1 a te d the ele c tro n s ta ti s ti Cs fo r the Pu rpo se o f s tu dying the do ping dependences of effective electron mass under the said conditions. We have plotted the effective mass with various physical variables, t aki rig n—Hg1CdTe a s an e x arnpl e whi c1 al so fi n d s e x ten si ye appl i Ca— tions as IR compounds and photovoltaic detector arrays. It is found that the effective masses increase with increasing electron concen— tration, oscillate with magnetic field and film thickness in various manners. The effective masses become juantui number dependent under crossed electric and magnetic field, quantuni wells under cross—field configurations and electric field aided quantum wires. The theoreti— cal results are in agreement with the experimental observations as given elsewhere. In addition, the eorsponding results of two—band Kane model and that of parabolic energy bands have been obtained from our generalized expressions as special cases under certain limiting condi tions.

Photoemission from quantum-confined structure of nonlinear optical materials

The photoemission from quantum wells, quantum wires, and quantum dots of nonlinear optical materials is studied, taking n-CdGeAs2 as an example. The authors have formulated the photoemission from the aforementioned materials by deducing the new carrier energy spectra in all cases, taking into account various types of anisotropies of the energy band parameters. It is found that the photoemission increases with incident photon energy in a ladder-like manner and also exhibits oscillatory dependences with changing film thickness and the carrier density, respectively, for all cases. The numerical values of the photoemission is greatest in quantum dots and least in quantum wells. The well-known results have been shown as special cases under certain limiting conditions of our generalized expressions. The theoretical formulations are in agreement with the experimental observations as reported elsewhere.

Heat capacity of MOS field-effect devices of optical materials in the presence of a strong magnetic field

In this paper, an attempt is made to study the heat capacity of MOS field-effect devices of optical materials under strong magnetic field using ternary compounds and nonlinear optical samples as examples of optical materials. The magneto-heat capacity of ternary materials is formulated in MOSFET by considering the fourth order in effective mass theory and taking into account the inter-actions of the conduction, heavy-hole, light-hole, and the split-off bands, respectively. The same capacity in nonlinear optical materials has also been formulated for the present case on the basis of newly-derived, generalized, 2-D carrier energy spectra by incorporating the anisotropic crystal potential and the Hamiltonian together with the anisotropies of the effective electron mass and the spin-orbit splitting parameter of the valence band for both the weak and strong electric field limits. The authors studied the surface electric field and the magnetic field dependences of the magneto heat capacity in n-channel inversion layers of the said materials taking n-Hg1-XCdXTe and CdGeAs2 as examples for both the limits. It is found that the magneto-heat capacity increases with magnetic field and surface field for both the limits in various types of oscillatory manners for all the cases. The theoretical results are in quantitative agreement with the experimental observation as reported elsewhere. In addition, the corresponding results of the magneto heat capacity for relatively wide-gap optical materials have been obtained from generalized expressions under certain limiting conditions.

Gate capacitance of MOS field effect devices of nonlinear optical materials in the presence of a parallel magnetic field

This paper studies the effect of a parallel magnetic field on the gate capacitance of MOS field- effect devices of tetragonal type of non-linear optical materials, taking n-Cd3As2 as an example. The expressions of the gate capacitances were derived for the present system for both the weak and the strong electric field-limits respectively. It was found, on the basis of newly derived generalized two-dimensional electron energy spectra by incorporating anisotropic crystal potential to the Hamiltonian together with the anisotropies of the effective electron mass and the spin-orbit splitting of the valence band within the domain of k. p theory, for both the limits, that the gate capacitances increases with increasing surface electric fields in an oscillatory manner. The gate capacitances also exhibit monotonous variations with increasing magnetic fields with different numerical values for both weak and strong field limits respectively. The theoretical results are in agreement with the experimental observation as reported elsewhere. In addition, the corresponding results of the gate capacitances in the absence of parallel magnetic field on the basis of our proposed dispersion law, three-band Kane model and two-band Kane model of MOS field-effect devices of nonlinear optical materials have been obtained.

Thermoelectric Power in Quantum Confined Optoelectronic Materials under Classically Large Magnetic Field

We shall study the thermoelectric power under classically large magnetic field (TPM) in optoelectronic materials of quantum wells (QWs), quantum well wires (QWWs), quantum dots (QDs) and compare the same with the bulk specimens of optoelectronic materials by formulating the respective electron dispersion law. The TPM increases with decreasing electron concentration in an oscillatory manner in all the cases, taking n-Hg 1−x Cd x Te as an example. The TPM in QD is greatest and the least for quantum wells respectively. The thecoretical results are in agreement with the experimental observations as reported elsewhere.

On the field emission from superlattices of small-gap materials with graded structures in the presence of a strong magnetic field

The field emission from III-V, II-VI, PbTe/PbSnTe, strained layer, and HgTe/CdTe superlattices with graded structures under magnetic quantization is investigated and compared with that of the bulk specimens of the constituent materials. The doping and magnetic-field dependences of the magneto-field emission of these superlattices are analyzed, and it is found that the field emission exhibits oscillatory dependences on the inverse magnetic field and electron concentration with more significant oscillations appearing in the HgTe/CdTe superlattices. Relations for the bulk specimens are obtained from the special cases of generalized formulations.

Diffusion coefficient of the minority carriers in quantum-confined lasers

of the electrons among tne size quantized levels. It may benoted that the quantum wire lasers produce very large changes in thediffusion constant. In quantum wire lasers, only one free directionof motion is allowed for the charge carriers. cbnsequently, thecrossing of the Fermi level by the size quantized subbands would havemuch greater impact on the redistribttion of the electrons among theallowed levels, as compared to found for quantum well lasers. Thediffusion

Effect of a longitudinal magnetic field on the diffusion coefficient of the minority carriers in solid state junction lasers

This paper discusses the diffusion coefficient of minority carriers in solid state junction lasers in the presence of a longitudinal quantizing magnetic field, i.e., III-V, II-VI and IV-VI lasers. An expression of the normalized diffusion coefficient of the minority carriers under magnetic quantization, spin, and broadening of Landau levels respectively, have been formulated without approximations of band parameters. The authors used three-band Kane model and the four-band Kane model for III-V lasers, Hopfield model for II-VI lasers, and the model of Genzow et al. for IV-VI lasers respectively. It was found, taking InSb, CdS, and PbTe junction lasers as examples of III-V, II-VI, and IV-VI lasers respectively, that the diffusion coefficient oscillates with inverse magnetic field for aforementioned lasers due to SdH effect. The diffusion coefficient continuously decreases at low temperatures with increasing values of the longitudinal magnetic field in the quantum limit. Unlike the decrease of the diffusion coefficient in a transverse magnetic field due to deflections of the minority carriers, the decrease in the longitudinal magnetic field results from the lowering of the electron quasi-Fermi level with respect to the bottom of the conduction band. The numerical magnitudes of the normalized diffusion constants are greatest for the II-VI lasers and the least for the III-V lasers. The theoretical results with experimental observations reported elsewhere. In addition, the results of wide band gap junction laser materials have been obtained as special cases of generalized formulations under certain limiting conditions.

Effect of magnetic quantization on the pulse power output of spontaneous emission for II-VI and IV-VI lasers operated at low temperature

In this paper an attempt is made to investigate the effect of magnetic quantization on tbe pulse power output of spontaneous emission from II-VI and IV-VI lasers operated at relatively low temperatures, on the assumption that the radiative recombination occurs through the recombination centers which obey the well-known Shockley-Read statistics, by formulating the magneto-dispersion laws of the said materials. We have studied the pulse power out-put in the presence of a quantizing magnetic field by considering the combined influences of spin and broadening of Landau levels. It is found, taking CdS laser and PbTe laser as examples, that the pulse power output exhibits oscillatory dependence and increases with increasing carrier density in an oscillatory way. It is also shown that the power output at both low and relatively higher operating temperatures may pass through a maximum or may continuously decrease with increasing magnetic field at the quantum limit. The corresponding results for wide-gap lasers have been obtained as special cases of our generalized formulations.