Growth and characterization of CdTe absorbers on GaAs by MBE for high concentration PV solar cells

Arı, Ozan; Polat, Mustafa; Karakaya, Merve; Selamet, Yusuf

doi:10.1002/pssc.201510068

Cited by 3 publications

(3 citation statements)

References 8 publications

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“…The tilt angles between the ZnTe and GaAs (211) substrates observed in our samples are less than the reported values in the literature for CdTe epilayers on GaAs (211) [36] and ZnTe films on Si (211) substrates [35]. For each sample we also calculated the average grain size, τ, of the crystallites along [0-11] direction from the Debye Scherer's formula:…”

Section: Resultsmentioning

confidence: 89%

Epitaxial characteristics of MBE-grown ZnTe thin films on GaAs (211)B substrates

Ozceri

Tarhan

2019

Appl. Phys. A

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Highly crystalline ZnTe thin films were grown on GaAs (211)B substrates by molecular beam epitaxy (MBE) for potential applications such as MCT detectors and optoelectronic devices. We investigated the effects of Te to Zn (VI/II) flux ratio on the quality of ZnTe films in terms of crystal orientation, elemental composition, surface roughness, and dislocation density. Atomic concentrations of Zn, Te, and oxygen complexes due to oxygen contamination on the film surfaces were analyzed by X-ray photoelectron spectroscopy. X-ray double crystal rocking curve full width half maximum (FWHM) of ZnTe (422) peak was observed as 233 arcseconds for a 1.66 μm thick film, which indicates high crystallinity. Wet chemical etching was applied to the films to quantify the crystal quality by calculating etch pit densities (EPD) from scanning electron microscope images. A very low EPD value of 1.7 × 10 7 cm −2 was measured. Additionally, the root mean square roughness values, obtained from atomic force microscopy topography images were in the range of 10-25 nm. These values were supported by FWHM values of red green blue color intensity histograms obtained from Nomarski Microscope images. The results of our analyses indicate that the VI/II flux ratios of 4 and 4.5 produce the best quality ZnTe films on GaAs (211)B substrates.

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Section: Resultsmentioning

confidence: 89%

Epitaxial characteristics of MBE-grown ZnTe thin films on GaAs (211)B substrates

Ozceri

Tarhan

2019

Appl. Phys. A

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“…The growth details were similar to those described elsewhere [11,12]. Briefly, CdTe epilayer was grown by molecular beam epitaxy (MBE) system operated in a class 1000 cleanroom environment on a 3-inch epi-ready, semi-insulating (2 1 1)B GaAs wafer after thermal stripping of the oxide layer.…”

Section: Molecular Beam Epitaxy (Mbe) Growth Of Cdtementioning

confidence: 99%

Reciprocal space mapping study of CdTe epilayer grown by molecular beam epitaxy on (2 1 1)B GaAs substrate

Polat¹,

Arı²,

Öztürk³

et al. 2017

Mater. Res. Express

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Reciprocal space mapping (RSM) has been widely utilized to find out the microstructure and deviations from ideal crystal structures, present in materials ranging from polycrystalline to single-crystalline [1]. RSM can deliver further structural information as compared to conventional methods such as rocking curve (RC) scan due to its two-dimensional (2D) characteristics [2]. This particularly provides a significant advantage when applied to epitaxial thin films having large lattice mismatches. Nondestructive measurement of the threading-dislocation (TD) densities, for instance, relies on prediction of individual parameters, such as domain tilt and twist, of a mosaic layer structure [3]. In addition to the large lattice mismatch, some epitaxial heterostructures have also the low-symmetry surface characteristics. CdTe/(2 1 1)B GaAs is obviously one of the outstanding examples of these types of structures. Structural analysis of the high-index oriented zinc-blende epitaxial layers when combined with the large lattice mismatch becomes much more challenging. Furthermore, the surface normal of epilayer lattice tilts approximately 3° with respect to that of substrate [4]. Each one of these factors make the structure being examined extremely difficult to analyze, especially with the traditional x-ray diffraction (XRD) methods. As a result, a limited number of studies so far have been dedicated to understanding the structural properties of this heterostructure [5][6][7][8]. The common point of all these studies is that they were carried out in real space. However, one advantageous option can be mapping in reciprocal space to characterize such heterostructures. At present, the technique has been separately applied to the high-index orientation [9] or to the large lattice mismatched heterostructures [10].In this letter, the RSM technique is effectively employed to study the lattice tilting, the lattice mismatches, the shear strain produced by the low-symmetry surface and the screw dislocation density of CdTe epilayer grown on (2 1 1) oriented GaAs substrate. Experimental procedure Molecular beam epitaxy (MBE) growth of CdTeThe growth details were similar to those described elsewhere [11,12]. Briefly, CdTe epilayer was grown by molecular beam epitaxy (MBE) system operated in a class 1000 cleanroom environment on a 3-inch epi-ready, semi-insulating (2 1 1)B GaAs wafer after thermal stripping of the oxide layer. Initially, a nucleation layer also

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“…Cadmium telluride (CdTe) grown on a highly latticemismatched GaAs substrate has attracted significant attention in various fields, ranging from low cost mercury cadmium telluride (MCT) infrared detectors, 1,2 solar cells 3 to nuclear radiation detectors. 4 Although remarkable progress has been achieved in epitaxial growth of CdTe thin films in recent years, 5 the lattice constant mismatch of approximately 14% at room temperature and the large difference in thermal expansion coefficients 6 still present considerable challenges for researchers.…”

Section: Introductionmentioning

confidence: 99%

Identifying threading dislocations in CdTe films by reciprocal space mapping and defect decoration etching

Polat

Bilgilisoy

Arı

et al. 2018

Journal of Applied Physics

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We study threading dislocation (TD) density of high-quality cadmium telluride (CdTe) layers grown on a (211) oriented GaAs substrate by molecular beam epitaxy. High-resolution X-ray diffraction was performed to calculate the density of screw-type TDs by measuring the broadening of the asymmetrical (511) Bragg reflections of CdTe epilayers. In addition, total TD densities were determined by the Everson-etching method and were compared with screw TDs. Our results show that the total TD densities in CdTe films were dominated by those with screw character. The screw component TDs are estimated to account for more than 90% of the total TD density.CdTe layers grown at a thickness of less than 3.0 lm typically exhibit the screw TD densities in the 10 6 cm -2 and 10 7 cm -2 range. It can be noted that as the nucleation temperature increases, i.e., !222 C, both the area density of TDs with the screw component of the CdTe films and the total TD density are roughly four times larger than those of the epilayer grown at the nucleation temperature of 215 C. Furthermore, we discuss the influence of the II/VI flux ratio on the density of threading dislocations. The contribution of screw TDs to the total TD density showed a significant decrease in roughly 30% in the case of a high II/VI flux ratio. We further examine the reciprocal space maps in the vicinity of the (422) reflections.

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Growth and characterization of CdTe absorbers on GaAs by MBE for high concentration PV solar cells

Cited by 3 publications

References 8 publications

Epitaxial characteristics of MBE-grown ZnTe thin films on GaAs (211)B substrates

Epitaxial characteristics of MBE-grown ZnTe thin films on GaAs (211)B substrates

Reciprocal space mapping study of CdTe epilayer grown by molecular beam epitaxy on (2 1 1)B GaAs substrate

Identifying threading dislocations in CdTe films by reciprocal space mapping and defect decoration etching

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