D.P. Bhattacharya

Electron transport in II-VI compound semiconductors

Abstract The mobility characteristics of II–VI compound semiconductors have been investigated using a displaced Maxwellian model for the energy distribution of the free carriers and considering the combined effects of acoustic, piezo-electric, ionised impurity and polar optical modes of scattering. The electric field dependence of the carrier mobility has been obtained at lattice temperatures of 77° K and 300°K. The effect of variation of the not too well known coupling constants on the characteristics has been observed. The variation of the low-field mobility with the lattice temperature and with the level of impurity concentration has also been obtained. The theoretical results agree quite satisfactorily with the available experimental data and with other theoretical works.

Effect of finite energy of deformation-potential acoustic phonons on the temperature of non-equilibrium carriers

Abstract The effect of the finite energy of the acoustic phonons on the temperature of the non-equilibrium carriers in pure semiconducting materials was investigated here by solving the energy balance equation for the electron phonon system at low lattice temperatures, without making the simplifying approximations of the traditional theory. The calculations were carried out for an isotropic material with a parabolic law of dispersion and a scalar effective mass. The field dependence of the electron temperature is now significantly different from what follows from the traditional theory, in which the phonon energy is neglected in comparison with the carrier energy. It is noted that the effect of the finite energy of the phonons on the carrier temperature at any field is greater the lower the lattice temperature. In comparison to the results of the traditional theory, the agreement of our results with the available experimental observations is found to be distinctly better. For a more detailed fit of the experimental results, the necessity of further refinements of the theory is discussed.

On the electron-phonon interaction in high purity semiconductors at low lattice temperatures

We discuss the question of neglecting the energy of the deformation acoustic phonons in the study of the electron-phonon interaction in highly pure semiconductors and show that this approximation leads to significant errors when the lattice temperature is low.

Mobility characteristics of non-equilibrium carriers in III–V compounds at low lattice temperatures

Abstract The effect of the finite energy of the deformation potential and piezoelectric acoustic phonons on the high-field mobility characteristics of n-type InSb and InAs at low lattice temperatures is calculated by a numerical method taking the non-parabolicity of the conduction band into account and under the conditions that the acoustic phonon energy cannot be neglected in comparison with the carrier energy and the phonon distribution cannot be represented by the equipartition law. The results are interesting in that they are significantly different from those that follow from the traditional approximation of negligible phonon energy and also provide good agreement with the available experimental data. The inadequacies of the present theory and the scope for further improvements are discussed.

Effect of screening on the carrier transport in semiconductors at low lattice temperatures

The effect of screening of the interaction potential by free electrons on the intravalley acoustic phonon scattering rate and zero field mobility characteristics of the electrons in a covalent semiconductor has been studied. The lattice temperature is assumed to be low when, unlike the traditional approximations, the energy of the acoustic phonons cannot be neglected nor can the phonon distribution be represented by the simple equipartition law. The same effect is also studied at high lattice temperatures where the traditional approximations are valid. It is seen that the screening effect changes the energy and temperature dependence of the scattering rates in significantly different ways at low and high temperatures. The resulting zero field mobility differs significantly at low temperatures compared to what follows from the traditional theory. Our numerical results for Si show that at low lattice temperatures the screening effect becomes as important as the effect of finite energy of the acoustic phonons.

An analysis of phonon emission as controlled by the combined interaction with the acoustic and piezoelectric phonons in a degenerate III–V compound semiconductor using an approximated Fermi–Dirac distribution at low lattice temperatures

Abstract Compound semiconductors being piezoelectric in nature, the intrinsic thermal vibration of the lattice atoms at any temperature gives rise to an additional potential field that perturbs the periodic potential field of the atoms. This is over and above the intrinsic deformation acoustic potential field which is always produced in every material. The scattering of the electrons through the piezoelectric perturbing potential is important in all compound semiconductors, particularly at the low lattice temperatures. Thus, the electrical transport in such materials is principally controlled by the combined interaction of the electrons with the deformation potential acoustic and piezoelectric phonons at low lattice temperatures. The study here, deals with the problem of phonon growth characteristics, considering the combined scattering of the non-equilibrium electrons in compound semiconductors, at low lattice temperatures. Beside degeneracy, other low temperature features, like the inelasticity of the electron–phonon collisions, and the full form of the phonon distribution have been duly considered. The distribution function of the degenerate ensemble of carriers, as given by the heated Fermi–Dirac function, has been approximated by a simplified, well-tested model. The model which has been proposed earlier, makes it much easier to carry out analytically the integrations without usual oversimplified approximations.

Field-effect mobility of a two dimensional electron gas in an n–channel of Si-SiO2 MOS structure with due consideration of some practical features

The field-effect mobility characteristics of a non-degenerate ensemble of a two dimensional electron gas for interaction with acoustic mode lattice vibrations in the Si-SiO2 MOS structure at the high surface electric fields are calculated here for the low and high temperature cases. The calculation takes due account of some features which are usually neglected. These include the effects of (i) the transverse component of the phonon wave vector, (ii) the realistic model of the infinite triangular potential well along the transverse direction, while applying the momentum conservation approximation, and (iii) the full form of the phonon distribution function at low temperatures. The results seem to be interesting in that they are significantly different from what follows from other theories that neglect the effects of the above features. Moreover, the agreement between the results which are obtained here with the experimental data seems to be significantly better. The scope for further refinement of the pres...

Microwave harmonics due to hot electrons in a magnetic field

The characteristics of Second Harmonic Generation (SHG) of microwaves in a covalent semiconductor at low lattice temperatures are studied here in the presence of a transverse, static magnetic field. The characteristics are estimated in the general case of any mechanism of energy and momentum scattering of hot carriers in the strong and weak magnetic field limits. Calculations are carried out with the approximations of a parabolic law of dispersion and a scalar effective mass. For some definite scattering mechanisms the characteristics are obtained in the presence of any finite value of the magnetic field. The presence of the magnetic field brings in significant changes in both qualitative and quantitative aspects of the characteristics. The results are useful to the determination of the predominant relaxation processes of the hot electrons under any prevalent condition.