A study of the properties of hydrogenated amorphous germanium produced by r.f. glow discharge as the electrode gap is varied the link between microstructure and optoelectronic properties

Wickboldt, P.; Jones, S.J.; Marques, F. C.; Pang, D.; Turner, W. A.; Wetsel, A. E.; Paul, William; Chen, J. H.

doi:10.1080/13642819108207628

Cited by 37 publications

(21 citation statements)

References 24 publications

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“…5,43 Arrhenius plots ͓log( d ) vs 1000/T͔ of the data often displayed slight nonlinearities at higher temperatures (1000/Tр2.5 K Ϫ1 ) and less often below room temperature (1000/Tу3.3 K Ϫ1 ). Samples deposited using extreme, unoptimized conditions often displayed entirely nonlinear Arrhenius plots.…”

Section: A Dark Conductivity Dmentioning

confidence: 98%

“…[40][41][42] The work presented in this article extends the earlier work on a-Ge:H 29,43,44 to a-Si 1Ϫx Ge x :H alloys for the range of 0.37рxр1.00. We present the results of a project in which we optimized the optoelectronic properties of a-Si 1Ϫx Ge x :H of large x, deposited by rf glow discharge CVD starting with conditions that are close to those optimized for a-Ge:H. This article is primarily concerned with the measured properties of these alloys and what can be learned from them, and not the deposition process or parameters.…”

Section: Introductionmentioning

confidence: 94%

“…The deposition system used and the details of sample preparation and measurement procedures have been described elsewhere. 43 The deposition system is a capacitively coupled diodetype rf glow discharge system. The samples were deposited on the cathode ͑powered electrode͒ and are referred to as cathodic material.…”

Section: Sample Preparation and Measurementmentioning

confidence: 99%

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High performance glow discharge a-Si1−xGex:H of large x

Wickboldt

Pang

Paul

et al. 1997

Journal of Applied Physics

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Radio frequency glow discharge chemical vapor deposition has been used to deposit thin films of a-Si1−xGex:H which possess optoelectronic properties that are greatly improved over any yet reported in the range of x⩾0.6. These films were deposited on the cathode (cathodic deposition) of an rf discharge. Their properties are assessed using a large variety of measurements and by comparison to the properties of alloys conventionally prepared on the anode (anodic deposition). Steady state photoconductivity measurements yield a quantum-efficiency-mobility-lifetime product, ημτ, of (1–3)×10−7 cm2 V−1 for 1.00⩾x⩾0.75 and (6–10)×10−8 cm2 V−1 for 0.75⩾x⩾0.50, and photocarrier grating measurements yield ambipolar diffusion lengths several times greater than previously obtained for alloys of large x. It is confirmed that the improvements in phototransport are not due to a shift in the Fermi level. In fact, results of recent measurements on lightly doped samples strongly suggest that for these cathodic alloys neither photocarrier is dominant [(μτ)e≈(μτ)h]. The improvements are attributed in large part to the reduction of long range structural heterogeneity observed in x-ray scattering and electron microscopy, and partly to the reduction in midgap state density. In spite of the superior properties, an assessment of the data of the cathodic alloys suggests that alloying introduces mechanisms detrimental to transport which are not present in a-Si:H or a-Ge:H. The Urbach tail width is 42±2 meV for cathodic a-Ge:H and 45±2 meV for cathodic a-Si1−xGex:H and is constant with x. From differences in the band edges and tails we infer that the atomic bond ordering is different between the cathodic and anodic alloys. For a given composition the cathodic alloys have roughly an order of magnitude lower midgap state density than do the anodic alloys, and both midgap densities increase exponentially with x, consistent with defect creation models from which the lower midgap density can be attributed to a larger band gap and decreased valence band tail width. A photoluminescence peak is observed with an intensity roughly an order of magnitude greater than for the anodic alloys, and a significantly different peak energy. Section VII E provides an overview of the results and conclusions. The improved properties of these alloys have significant implications for current and future device applications.

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Section: A Dark Conductivity Dmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 94%

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High performance glow discharge a-Si1−xGex:H of large x

Wickboldt

Pang

Paul

et al. 1997

Journal of Applied Physics

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“…a-Ge:H has a low band gap absorber with regard to the a-Si:H, thus giving these materials a better exploitation of the solar spectrum and achieve higher efficiencies [2]. Many authors [3,4] have shown that the optoelectronic properties of a-Ge:H deposited by PECVD technique on the powered electrode (cathode) were dramatically superior to those films deposited on the unpowered electrode (anode) conventionally used for deposited device quality a-Si:H. The ameliorations have been attributed, mainly, to the high ion bombardment energy at the cathode surface. The benefits of the dilution of the germane gas (GeH 4 ) in hydrogen have been demonstrated for the improvement of the properties of a-Ge:H. The (a-Ge:H) films deposited by this technique at a high rate show an improved reproducibility, i.e., films thicknesses are more uniform and a reduced light induced degradation with regard to other methods [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Films thickness effect on structural and optoelectronic properties of hydrogenated amorphous germanium (a-Ge:H)

Belfedal

Bouizem

Sib

et al. 2012

Journal of Non-Crystalline Solids

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“…The intensity of the thermal stress also depends on the elastic modulus; ͑2͒ the filmϩsubstrate interface is also a source of stress, known as interfacial stress, which appears due to differences between structural properties of the film and substrate; and ͑3͒ the growth mechanism generates stress in the bulk of the films, the intrinsic stress, which depends on the technique used and on the preparation conditions. 3,4 It is well accepted that the intrinsic tensile stress is due to some sort of defect, especially voids and columnar structures. The origin of the compressive stress, on the other hand, is not clear yet, but it is apparently associated with the presence of contaminants, such as argon, oxygen, and hydrogen.…”

Section: Introductionmentioning

confidence: 99%

Coefficient of thermal expansion and elastic modulus of thin films

Lima

Lacerda

Vilcarromero

et al. 1999

Journal of Applied Physics

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138

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The coefficient of thermal expansion ͑CTE͒, biaxial modulus, and stress of some amorphous semiconductors ͑a-Si:H, a-C:H, a-Ge:H, and a-GeC x :H͒ and metallic ͑Ag and Al͒ thin films were studied. The thermal expansion and the biaxial modulus were measured by the thermally induced bending technique. The stress of the metallic films, deposited by thermal evaporation ͑Ag and Al͒, is tensile, while that of the amorphous films deposited by sputtering ͑a-Si:H, a-Ge:H, and a-GeC x :H͒ and by glow discharge (a-C:H) is compressive. We observed that the coefficient of thermal expansion of the tetrahedral amorphous thin films prepared in this work, as well as that of the films reported in literature, depend on the network strain. The CTE of tensile films is smaller than that of their corresponding crystalline semiconductors, but it is higher for compressive films. On the other hand, we found out that the elastic biaxial modulus of the amorphous and metallic films is systematically smaller than that of their crystalline counterparts. This behavior stands for other films reported in the literature that were prepared by different techniques and deposition conditions. These differences were attributed to the reduction of the coordination number and to the presence of defects, such as voids and dangling bonds, in amorphous films. On the other hand, columnar structure and microcrystallinity account for the reduced elasticity of the metallic films.

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A study of the properties of hydrogenated amorphous germanium produced by r.f. glow discharge as the electrode gap is varied the link between microstructure and optoelectronic properties

Cited by 37 publications

References 24 publications

High performance glow discharge a-Si1−xGex:H of large x

High performance glow discharge a-Si1−xGex:H of large x

Films thickness effect on structural and optoelectronic properties of hydrogenated amorphous germanium (a-Ge:H)

Coefficient of thermal expansion and elastic modulus of thin films

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