Optical characterization of epitaxial single crystal CdTe thin films on Al2O3 (0001) substrates

Jovanovic, Stephen M.; Devenyi, Gabriel A.; Jarvis, Victoria; Meinander, Kristoffer; Haapamaki, Chris M.; Kuyanov, P; Gerber, Martin; LaPierre, Ray; Preston, J. S.

doi:10.1016/j.tsf.2014.09.027

Cited by 7 publications

(5 citation statements)

References 29 publications

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“…It has been previously demonstrated that single crystal thin films of CdTe can be grown on the basal plane of sapphire substrates, which have similar or higher quality than their bulk substrate counterparts. [ 10,11 ] The most stable surface reconstruction of α‐Al 2 O 3 (0001) is a single Al‐termination (Figure S1, Supporting Information), which is nonpolar. [ 12,13 ] This surface has sixfold rotational symmetry and thus geometrically, there are two‐possible in‐plane domain rotations for a threefold CdTe system to align as seen in Figure a.…”

Section: Figurementioning

confidence: 99%

Spontaneous Relaxation of Heteroepitaxial Thin Films by van der Waals‐Like Bonding on Te‐Terminated Sapphire Substrates

Jovanovic

El‐Sherif

Bassim

et al. 2020

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Heteroepitaxy of thin film materials is a fundamental industrial process for the fabrication of high-quality electronic and electrooptic devices. Conventionally, strong bonding of adatoms on a substrate leads to a coherent thin film below a critical thickness, where the thin film grows strained from its relaxed lattice spacing. Above this critical thickness strain is relieved by defect generation in the thin film. Commercial development of heteroepitaxial technologies is limited by both the availability and cost of lattice-matched substrates. This lattice matching requirement is diminished for van der Waals (vdW) heteroepitaxial systems due to weak interlayer

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Section: Figurementioning

confidence: 99%

Spontaneous Relaxation of Heteroepitaxial Thin Films by van der Waals‐Like Bonding on Te‐Terminated Sapphire Substrates

Jovanovic

El‐Sherif

Bassim

et al. 2020

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“…Specific candidates of opaque NTE films include metallic perovskite ReO 3 (Chatterji et al, 2009a;Chatterji et al, 2009b;Rodriguez et al, 2009), semiconducting Sm 0.8 Y 0.2 S (Takenaka et al, 2019;Mazzone et al, 2020), and insulating Si (Shah and Straumanis, 1972) or CdTe (Greenough and Palmer, 1973;Jovanovic et al, 2014) at low temperature at pump photon energies exceeding their band gap (1 and 1.51 eV at 300 K respectively (Bludau et al, 1974;Jovanovic et al, 2014)). Given recent advances in high-harmonic generation of laser sources, any NTE material could be considered if the photon energy exceeds the candidate material band gap.…”

Section: Results: Strain Waves Produced In Materials With Negative Thermal Expansionmentioning

confidence: 99%

Soliton Generation in Negative Thermal Expansion Materials

et al. 2021

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Strain solitons have been observed statically in several 2D materials and dynamically in substrate materials using ultrafast laser pulses. The latter case relies on lattice relaxation in response to ultrafast heating in a light-absorbing transducer material, a process which is sensitive to the thermal expansion coefficient. Here we consider an unusual case where the sign of the thermal expansion coefficient is negative, a scenario which is experimentally feasible in light of rapid and recent advances in the discovery of negative thermal expansion materials. We present numerical solutions to a nonlinear differential equation which has been repeatedly demonstrated to quantitatively model experimental data and discuss the salient results using realistic parameters for material linear and nonlinear elasticity. The solitons that emerge from the initial value problem with negative and positive thermal expansion are qualitatively different in several ways. The new case of negative thermal expansion gives rise to a nearly-periodic soliton train with chirped profile and free of an isolated shock front. We suggest this unanticipated result may be realized experimentally and assess the potential for certain applications of this generic effect.

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“…The mechanism of the passivation is not yet clear but could be due to a high density of fixed negative charge or the low degree of lattice mismatch (3.7%) between the unit cell of the (0001) surface of Al 2 O 3 and the (111) surface of CdTe . These characteristics offer the potential for repelling minority carriers and creating a low defect density interface, respectively. ,,, …”

Section: Introductionmentioning

confidence: 95%

“…19 These characteristics offer the potential for repelling minority carriers and creating a low defect density interface, respectively. 16,18,20,21 While demonstration of long carrier lifetimes via an optical measurement is promising, to date there is no clear evidence for back-surface passivation in an operating CdTe device. Previous attempts have included deposition of alumina by atomic layer deposition (ALD) 22 and sputtering.…”

Section: ■ Introductionmentioning

confidence: 99%

Back-Surface Passivation of CdTe Solar Cells Using Solution-Processed Oxidized Aluminum

Alfadhili

Phillips

Subedi

et al. 2020

ACS Appl. Mater. Interfaces

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Although back-surface passivation plays an important role in high-efficiency photovoltaics, it has not yet been definitively demonstrated for CdTe. Here, we present a solutionbased process, which achieves passivation and improved electrical performance when very small amounts of oxidized Al 3+ species are deposited at the back surface of CdTe devices. The open circuit voltage (V oc ) is increased and the fill factor (FF) and photoconversion efficiency (PCE) are optimized when the total amount added corresponds to ∼1 monolayer, suggesting that the passivation is surface specific. Addition of further Al 3+ species, present in a sparse alumina-like layer, causes the FF and PCE to drop as the interface layer becomes blocking to current flow. The optimized deposit increases the average baseline PCE for both Cu-free devices and devices where Cu is present as a dopant. The greatest improvement is found when the Al 3+ species are deposited prior to the CdCl 2 activation step and Cu is employed. In this case, the best-cell efficiency was improved from 12.6 to 14.4%. Time-resolved photoluminescence measurements at the back surface and quantum efficiency measurements performed at the maximum power point indicate that the performance enhancement is due to a reduction in the interface recombination current at the back surface.

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Optical characterization of epitaxial single crystal CdTe thin films on Al2O3 (0001) substrates

Cited by 7 publications

References 29 publications

Spontaneous Relaxation of Heteroepitaxial Thin Films by van der Waals‐Like Bonding on Te‐Terminated Sapphire Substrates

Spontaneous Relaxation of Heteroepitaxial Thin Films by van der Waals‐Like Bonding on Te‐Terminated Sapphire Substrates

Soliton Generation in Negative Thermal Expansion Materials

Back-Surface Passivation of CdTe Solar Cells Using Solution-Processed Oxidized Aluminum

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