Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit

Analysis is made for the possibility of redistribution of mobile point defects in a semiconductor after its exposure to the electric field till the stationary conditions in the crystal are reached. Two different ways of applying the voltage are considered: (i) directly to the sample, (ii) to a capacitor, with the sample located between the plates. This model is applicable also to the electric field of any nature, whether external or internal, e.g. that arisning at the metal-semiconductor interface.Дається аналіз можливості розподілу рухомих точкових дефектів в напівпровіднику після дії на нього електричного поля до встановлення стаціонарних умов. Розглядаються два способи прикладання напруги: а) безпосередньо до зразка, б) до обкладинок конденсатора, між якими поміщається зразок. Модель також можна застосовувати для електричних полів будь-якої природи . як зовнішніх так і внутрішніх, що виникають, наприклад, на контакті метал-напівпровідник.Приводится анализ возможности распределения точечных дефектов в полупроводнике после воздействия на него электрического поля до установления стационарных условий. Рассматривается два способа приложения напряжения: а) непосредственно к образцу, б) к обкладкам конденсатора, между которыми помещается образец. Модель также применима для электрических полей любой природы как внешних так и внутренних, возникающих, например, на контакте металл-полупроводник

The nature of red emission in porous silicon

The photoluminescence spectra of porous silicon at 77 and 300 K and their transformation during aging were investigated. The competition of two radiative recombination channels that have a common excitation mechanism was observed. It is shown that only one of them, which causes infrared emission band and is present in as-prepared samples, is connected with excitonic recombination in Si nanocrystals. The second one that causes red emission band appears during aging is supposed to be connected with carrier recombination through oxide-related defects. It is shown that this channel dominates in aged samples

Properties of the shallow D-centers in semiconductors with polar and covalent binding

The theoretical consideration of the energy of the lowest singlet and triplet terms of shallow D¯-centers (two electrons, bound with one-charge Coulomb center) in semiconductors with an ionic and covalent binding has been carried out. The electron-phonon interaction is described by a Frцhlich Hamiltonian. The energy of D¯-center is described with the use of a Buimistrov-Pekar method of canonical transformations for arbitrary electron-phonon coupling. It is shown, that for all area of electron-phonon interaction parameters the Buimistrov-Pekar method yields the lowest values of the ground state energy of D¯-centers and free bipolaron in comparison with the best, for today, numerical calculations of the relevant values which have been carried out within the framework of the direct variation methods. The calculations have shown the lack of the bound metastable triplet states corresponding to the lowest triplet energy term of D¯-center and bipolaron for all the area of electron-phonon interaction parameters, in complete analogy to the Hill theorem about the lack of the bound excited states of H¯ ion. It is shown that the account of interaction with acoustic phonons can produce considerable lowering the ground state energy of D¯-center in comparison with the magnitude 1.0555Ry

Influence of cation vacancy related defects on the self-assembly processes in CdSe/ZnSe quantum dot heterostructures

A spatial distribution of the cation vacancy related defects and their influence on the formation processes of self-assembled nanoislands in CdSe/ZnSe heterostructures were investigated by photoluminescence methods. Self-assembling growth was achieved under low temperature (2300C) molecular beam epitaxy with a subsequent annealing step. To change a number of cation vacancy related defects a VI/II beam pressure ratio РVI/РII was varied from 2:1 to 5:1. In the samples grown under РVI/РII = 5:1 a significant increase of self activated emission band caused by cation vacancy related defects was found. A study of the excitation spectra of defect related band revealed that in all samples the cation vacancy related defects are present in ZnCdSe wetting layer. In the samples grown under РVI/РII = 5:1 they were observed on nanoisland interface too. It was found that the increase of Se beam pressure results also in high energy shift and narrowing of nanoisland emission band. This process is accompanied by low energy shift of ZnSe band-to-band emission. Observed changes in photoluminescence spectra are explained by the decrease of Cd content in ZnCdSe layer due to enhancement of Cd/Zn interdiffusion process in the result of the increase of vacancy related defect number

About the nature of diffusion anisotropy in CdS crystals

Electrodiffusion of copper into nominally undoped high-resistivity CdS crystals at 250-400°C has been investigated. A strong diffusion anisotropy has been observed, copper diffusion in perpendicular to the c-axis direction being more than one order faster as compared with its diffusion in parallel to the c-axis direction. The effect has been shown to be not due to greater density of perpendicular to the c-axis dislocations than that of parallel to the c-axis ones, as it was thought earlier. Electrically active dislocations lying in the basal plane are supposed to be channels of fast diffusion owing to their intensive decoration with intrinsic defects and residual impurities

Role of Ionic Processes in Degradation of Wide-Gap II-VI Semiconductor Materials

A role of mobile defects in processes responsible for II-VI compound semiconductor characteristic instability is under consideration. These defects have been shown to be responsible for electron-enhanced reactions in these materials, in particular, shallow donor creation in CdS crystals. Accumulation of mobile defects near dislocations results in some specific effects: anisotropy of conductivity induced by electric field and distortion of edge emission spectrum shape. These effects side by side with electron-enhanced defect reactions have been found to influence considerably semiconductor device characteristics