Anisotropic Lattice Relaxation and its Mechanism of ZnSe Epilayer Grown on (001) GaAs Substrate by Molecular Beam Epitax
- PDF / 378,225 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 50 Downloads / 156 Views
epitaxial
layer
of
1.5
ftm
thickness
were
grown
by
449 Mat. Res. Soc. Symp. Proc. Vol. 399 01996 Materials Research Society
molecular
beam
epitaxy(MBE) at 300' C . A (001)-oriented GaAs wafer were used as a substrate. In order to study the lattice deformation of the MBE grown ZnSe epilayer, double-crystal X-ray rocking curves were measured using Cu K0 radiation. Rocking curves for (004) symmetric and {115), {404} asymmetric reflections were measured as a function of azimuthal rotation angle a of the sample. The azimuthal rotation is defined as a clockwise rotation around [001] direction of the sample. At a=0, the projections of the incident and the reflected X-ray beam lie along [110] direction. Lattice spacing perpendicular to the interface was measured from rocking curves for (004) reflection, while in-plane spacings along and directions were determined from {115) and {404} rocking curves, respectively. RESULTS AND DISCUSSION In a double-crystal rocking curve, the angular separation wco(a) of two peaks corresponding to the substrate and the epilayer, respectively, as a function of the azimuthal angle a consists of three components.
Ao,(a) = AdO + zo(a) + P(a)
(1)
where dO is the difference in Bragg angle due to the difference in interplanar spacings between the substrate and the epilayer, Aq5(a) the difference in tilt of the substrate and the epilayer due to the tetragonal distortion of the epilayer unit cell, and Q(a) the misorientation angle between two [001] directions of the substrate and the epilayer. For (004) symmetric reflections Jqo(a) is 0, and the peak splitting Awc(a) is affected by AO and Q(a). For {115} asymmetric reflections Fig. 1 shows schematically the influence of Aq0 and S2 on the splitting Aw(a) as a function of the angle a . Fig. la represents the glancing exit condition (Oi= OB÷ + ) at a =00, while Fig. lb the glancing incidence condition (di= O,-O ) at a =180', where Oi is the incidence angle of
layer
A0 +f2f
A0 - f2
substrate -
Ao =AOA + A +,2
A,=AO-A0
(a)
-A 2
(b)
Fig. 1. Schematic representation of X-ray diffraction conditions for {115) reflections. a) glancing exit condition at a =0' , b) glancing incidence condition at a =180'
450
X-ray beam, dB the Bragg angle of the plane and 0b the angle between (115) and (001) planes. In Fig. 2 two (004) rocking curves measured at two different azimuthal angles of the sample are shown. (004)o and (004), represent the rocking curves corresponding to the azimuthal angles a=0, and a=180' , respectively. The peak separations for the curves (004)o and (004),, are unequal. Fig. 3 shows the variation of the peak separations Aw(a) measured from (004) reflections as a function of the angle a. The solid-line in the figure represents a least-squares fit to the experimental data. Ajw(a) vary sinusoidally with a period of 360' , indicating that the epilayer is tilted with respect to the GaAs substrate.[ll] The epilayer is tilted along [1101 direction corresponding to the angle a =0' and the misorientation angle £2 of the epilayer w
Data Loading...
