Scattering mechanisms of electrons in ZnSe crystals with high mobility

Physica Status Solidi (b)

et al. 2003

Self Cite

Temperature dependence of electron mobility in n-ZnSe single crystals is investigated in the temperature range 77-300 K. A comparative analysis of experimental data with the known theoretical dependences calculated using solution of the Boltzmann transport equation and taking into consideration all major scattering mechanisms and screening effects is carried out. The good agreement between the experimental and theoretical dependences of electron mobility on both temperature and electron concentration is observed for the samples with various compensation ratios. It is shown that parameters such as the ionized impurity concentration and acceptor concentration can quickly be estimated for strongly compensated samples.В интервале температур от 77 до 300 К исследована температурная зависимость подвижности электронов в монокристаллах n-ZnSe. Проведен сопоставительный анализ экспериментальных данных с известными теоретическими зависимостями, полученными из решения кинетического уравнения Больцмана с учетом основных механизмов рассеяния и процессов экранирования. Наблюдается хорошее согласие экспериментальных и рассчитанных зависимостей подвижности электронов от температуры и концентрации носителей тока с учетом различной степени компенсации примеси. Показано, что для сильно компенсированных образцов может быть сделана экспресс-оценка таких параметров, как концентрация ионизированной примеси и концентрация акцепторов.

Section: Introductionmentioning

confidence: 58%

“…They have concluded that the acoustic type of scattering is not essential. It was shown later [3] that acoustic-phonon scattering can considerably limit carrier mobility at high temperatures if the value of the deformation potential is equal to 11.5 eV.…”

Section: Introductionmentioning

confidence: 98%

Electron mobility in ZnSe single crystals

Avdonin

Physica Status Solidi (b)

et al. 2003

Self Cite

“…The electron mobility in samples annealed in zinc at T b 800 C has a dark value of 520 cm 2 /Vs at room temperature, indicating the high perfection and purity of the original crystal [8]. With temperature decrease, the mobility monotonously increases in conformity with a power law (Fig.…”

mentioning

confidence: 82%

“…Temperature dependence of electron conductivity for the n-ZnSe : Zn samples ( * dark, * illumination). Annealing temperature: (1) 950, (2) 900, (3) 800, (4) 700, (5) 675, (6) 650, (7) 620, (8) 600 C concentration of the V Se which are shallow donors with an ionization energy of % 10 meV. Thus, the observed increase of the concentration of the shallow donor and the decrease of their ionization energy to 9 meV, as the annealing temperature increases, are the consequence of a sharp increase of the V Se native defect concentration.…”

Section: à3mentioning

confidence: 99%

Native Defect Nature of Electrical Centres in Low-Resistivity Zinc Selenide

Kasiyan

1998

phys. stat. sol. (b)

Hall effect, electric conductivity and electron mobility in n-ZnSe crystals, annealed in Zn melt at temperatures from 500 to 950 C, are studied in the temperature range from 55 to 500 K. The sharp increase of the shallow donor concentration is accompanied by a decrease of their compensation from K N A aN D 0X91 to 0.35, and of the activation energy E D from 28 to 9 meV, as the annealing temperature of n-ZnSe crystals increases above 650 C. At low annealing temperatures, the conductivity of n-ZnSe is determined by shallow non-controlling donors such as Al Zn , Ga Zn , In Zn . The concentration of V Zn native defects compensating the shallow donors is sharply decreased and the concentration of the V Se shallow donors determining the conductivity of crystal is sharply increased, as the annealing temperature increases above 800 C. The decrease of annealing temperature of the samples below 650 C results in a drastic decrease of the conductivity of the crystal, a decrease of electron concentration, and abnormally low mobility values. The observed anomalies of transport effects are found to be caused by the presence of a random potential relief in n-ZnSe samples.ZnSe single crystals grown by various methods have a high resistivity r % 10 8 to 10 10 W cm, as they are strongly compensated [1 to 3]. High-temperature annealing in liquid Zn sharply reduces their resistivity [4]. It was supposed previously that the increase of conductivity in the process of such a thermal treatment is caused by a decrease of the degree of compensation of unknown shallow donors, the concentration of which is changed slightly. On the other hand, the result of excitonic spectroscopy of n-ZnSe crystals annealed in a Zn melt have convincingly shown that occupation of acceptor defects V Zn leads to a generation of the shallow donor V Se [5]. In this work, we show that native donor type defects, selenium vacancies, whose compensation increases sharply during such annealing, are the shallow donors determining the high conductivity of n-ZnSe crystals annealed in a Zn melt.The n-ZnSe samples were prepared by long-term (100 h) high-temperature (from 500 to 950 C) treatment of the originally high-ohmic r % 10 10 W cm monocrystals in a zinc alloy. After the treatment, the samples were instantaneously cooled down to 20 C. Zn diffusion in ZnSe is caused by Frenkel-type defects, and the self-diffusion coefficient D Zn does not depend on the partial pressure of the components above the solid phase. In the temperature range from 750 to 1150 C and the Zn vapor pressure range of 10 mPa to 80 kPa, the self-diffusion coefficient is D Zn (cm 2 as 9X8 exp À3X0 eVakT).

“…On the dielectric side of the M±I transition, as the temperature decreases from room temperature to 100 K, the resistivity falls down and is determined by the scattering of charge carriers by optical phonons with a considerable polaron screening of this process [7]. The increase of the impurity concentration in the samples shifts the minimum in the dependence rT to higher temperatures.…”

mentioning

confidence: 98%

Metal-Insulator Transition Induced by Shallow Donor Impurity in n-ZnSe

Kasiyan

1998

phys. stat. sol. (b)

The resistivity and Hall coefficient of n-ZnSe monocrystals were investigated in the region of the metal±insulator (M±I) transition induced by variation of shallow donor impurity Al concentration from 2 Â 10 16 to 2 Â 10 18 cm À3 . It has been found that the transition from an activated conduction to a metallic one occurs at donor concentration 1X3 Â 10 17 cm À3 and takes place within the impurity band before it merges with the bottom of conduction band. On the dielectric side of the M±I transition the conduction with an activation energy e 1 induced by electron excitation from the impurity states into the conduction band is replaced by the hopping conduction with a constant activation energy e 3 which, in the lowest temperature region, is changed to a hopping conduction with variable activation energy.The principal feature of the theory of metal±insulator (M±I) transitions is the variation of the metallic conductivity as well as other parameters near the transition at zero temperature. Starting from the qualitative analysis of conductivity in the Anderson model, Mott [1] has predicted a sharp drop of metallic conduction to zero at the M±I transition and therefore the existence of a minimum metallic conductivity s mm lim n3n c s0. Cohen [2] advanced an alternative of a continuous attenuation of metallic conduction to zero at the M±I transition starting from the analogy of localization with percolation [3]. To investigate the M±I transition in doped semiconductors it is convenient to use the axial compression or a strong magnetic field which allow us to vary the radius of the electron wave function without changing the real concentration of impurities and the character of their distribution in the crystal [4 to 6].In this paper an attempt is made to obtain a M±I transition in ZnSe, in which the Bohr radius of the impurity is about 2.7 nm due to a certain change of the shallow donor concentration (aluminium impurity). With that in view, the n-ZnSe samples were Al-doped by long-term (100 h), high-temperature (T 950 C) treatment of the originally high-ohmic (r % 10 8 to 10 10 W cm) monocrystals in the Al + Zn alloy with varying aluminium percentage (from 0.05 to 1.25 at.%). The crystals were annealed in sealed ampoules at % 1X33 Â 10 À2 Pa, which were placed in a vertical furnace. In the temperature range from 1.6 to 300 K the temperature dependencies of resistivity, Hall coefficient and electron mobility are investigated in samples with concentration of shallow donor impurity varying within the limits of 2 Â 10 16 and 2 Â 10 18 cm À3 . In Fig. 1, a series of curves of the temperature dependence of resistivity for the investigated n-ZnSe samples is given. It is seen that as the donor concentration increases the slopes of the low-temperature and high-temperature portions of the rT dependence