T. Yoshiie

Polarity identification of CdTe crystallites

Abstract The crystal polarity of CdTe with the zincblende structure has been shown to be identifiable by triangular etch pits developed on the {110} plane which is easy to obtain as the cleavage plane or the growth habit plane. Examples are given of identifying the growth polarity of as-grown crystallites.

Orientation dependence of electron–irradiation damage in zinc oxide

Abstract The threshold voltage for zinc displacement in ZnO by electron irradiation lias been determined by high–voltage electron microscopy as a function of incident orientation from the [2110] to both the [0001] and [000T] directions. It is found that the threshold voltage is a minimum (∼700kV) in the [2110] direction and a maximum (∼1100kV) in the [0001] and [000T] directions without showing polarity effects. The result is interpreted in terms of the crystal structure of ZnO.

Irradiation damage of II–VI compounds in a high-voltage electron microscope

Abstract Dislocation loops produced by electron irradiation in a 1 MV electron microscop have been studied above room temperature for five II-VI compounds: CdS and ZnO, with the wurtzite structure, and CdTe, ZnSe and ZnS, with the zincblende structure. For all the crystals the density of loops decreased as the irradiation temperature increased, until no loops were produced above a certain temperature which varied from crystal to crystal. However, the loop density did not depend on the electron flux intensity, suggesting the heterogeneous nucleation at some impurity complex of equilibrium concentration. Diffraction contrast analyses showed that the loops are of interstitial type in each crystal, with Burgers vectors as follows: 1/2[0001] and 1/3〈1120〉 for wurtzite crystals, the density ratio of the former type to the latter being increased with increasing temperature; mostly 1/3〈111〉 and a few 1/2〈110〉 for zincblende crystals, the latter type being presumably formed as a result of unfaulting in the former....

Growth mechanism of hollow CdSe and CdS crystals

Abstract Hollow CdSe and CdS crystals with many striations parallel to the c direction on their side surface were obtained by the sublimation method. Proposed growth mechanisms for these hollow crystals are as follows: hollow CdSe crystals are composed of many c -needles grown on the lateral surface of an initial c -needle. The c -needles are developed from c -whiskers. These c -needles are united into a wall, leaving a cavity at its center. On the other hand, hollow CdS crystals are grown by a combination of several crystal walls extending from previously grown walls. Each wall is developed from an array of c -whiskers. As the result of such combination of crystal walls several cavities are left in the crystal.

Studies of dislocation loops produced by irradiation of ZnO in a high-voltage electron microscope

Abstract Electron-irradiation studies on vapour-grown ZnO ribbon crystals have been carried out in situ in a high-voltage electron microscope. Dislocation loops nucleate both on stacking-fault planes and in the matrix by irradiation with electron accelerated through voltages higher than 700 kV at room temperature. Two types of loops with the Burgers vectors b = 1/2c and b = a exist in the matrix, where a = 1/3 and c = [0001]. On the other hand, loops with b = 1/2 c + a/3 and those with b = 1/2c are formed on the prismatic fault planes and basal fault planes, respectively. Diffraction-contrast experiments show these loops to be of interstititial type. A re-irradiation experiment after the annealing indicates a possibility that there exist vacancies in the matrix at 700°C.

Polarity of CdS crystals growing in atmosphere of excess Cd or S vapor

Abstract CdS needle crystals were grown in an atmosphere containing excess Cd or S vapor by the sublimation method, and the polarity of their growth direction was identified by etching their top polar surface. The dominant growth direction of the crystal along the polar axis in an atmosphere of excess Cd vapor is the 〈0001〉, and it is the 〈0001〉 in an atmosphere of excess S vapor.

Effects of an electric field on the growth of CdS crystals

Abstract CdS crystals were grown from the vapor under an electrostatic field. When the potential of a central electrode was kept at a value less than minus several tens of volts, crystals grew preferentially in the + c -direction on the central electrode placed in the growth zone, but they grew preferentially in the - c -direction when the potential was kept at a higher value than that value. These growth features are the same when crystals were grown on the polar surface of a CdS substrate fixed on the central electrode. These results suggest that the electrostatic field accelerates the preferential deposition of one of the ionized constituent atoms onto the growth surface and causes a difference in the growth rate between two polar surfaces.

Effect of oxygen on the growth of ZnO crystals along the polar axis

Abstract ZnO needles were grown from ZnSe vapour by chemical reaction with oxygen, and the polarity of their growth direction along the c axis was studied with varying oxygen flow rate. The - c growth type needles and the + c growth type needles have been obtained at higher and lower flow rates of oxygen gas, respectively.

Effect of crystal polarity on irradiation-produced secondary defects in CdTe

Abstract Electron irradiation of CdTe in a high voltage electron microscope produced faulted dislocation loops on {111} plane with a triangular shape oriented in one direction, which reflects the crystal polarity. The loops are of interstitial type and bounded only by one type of the Frank partial or the α-Frank partial. The result is discussed in terms of a possible difference in the core structure between α- and β-Frank partials.

Effect of an electric field on the polarity of growth direction in CdSe and ZnO crystals

Abstract CdSe and ZnO needles were grown under an electric field. The electric field applied in the growth zone plays an important role for the polarity of growth direction along the c axis in both CdSe and ZnO crystals. The conditions for obtaining the + c or - c growth needle are given.