Electron and hole μτ products of slightly doped a-Ge:H films

Kusian, W.; Pfleiderer, H.-J.; Günzel, E.

doi:10.1016/s0022-3093(05)80244-3

Cited by 18 publications

(7 citation statements)

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“…We may say that both L amb and display an extremum for zero doping. These data are analogous to those presented by Yang et al 75 for anodic a-Si:H and anodic a-Si 1Ϫx Ge x :H and by Kusian et al 106 for cathodic a-Ge:H, and we interpret our data in the same manner as they did. As follows from Eqs.…”

Section: Methodssupporting

confidence: 92%

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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: Methodssupporting

confidence: 92%

“…These different transport properties may, in large part, be caused by differences in the Fermi level. Typically, 75,106 it is necessary to move the Fermi level closer to the valence band through p-type doping in order to achieve the conditions given in Eq. ͑A1͒.…”

Section: Ph 3 and B 2 H 6 Doping Results/interpretationmentioning

confidence: 99%

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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“…For the undoped sample, N D is dominated by D 0 states, with a small contribution of D Ϫ and negligible ͓D ϩ ͔. Combining the photocarrier grating technique and photoconductivity measurements, Kusian et al 17 found a () n product 100 times larger than the () p product in undoped a-Ge:H. A similar result is observed in undoped a-Si:H. 16 Hence, the measured product, which is the sum of the contributions of excess electrons and holes, is dominated by the electron contribution. As the Ga concentration increases through region I, D Ϫ decreases by three orders of magnitude, while D ϩ increases by one and a half orders of magnitude.…”

Section: Discussionmentioning

confidence: 99%

“…The dependence of the PC on doping in a-Si:H has been reported in the literature, especially for phosphorusand boron-doped samples. [14][15][16] Much less work has been done for doped a-Ge:H. Kusian et al 17 measured the PC of B-doped a-Ge:H films ͑using B 2 H 6 as the dopant source͒ deposited by the glow-discharge method. Marcano et al 13 have reported on the PC of nitrogen-doped a-Ge:H films deposited by rf sputtering.…”

Section: Introductionmentioning

confidence: 99%

Steady-state photoconductivity of gallium- and indium-doped hydrogenated amorphous germanium thin films

Reis

Comedi

Chambouleyron

1998

Journal of Applied Physics

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The effects of gallium and indium p-type doping on the photoconductivity of hydrogenated amorphous germanium ͑a-Ge:H͒ thin films deposited by the rf-sputtering method are reported. The quantum efficiency-mobility-lifetime ͑͒ product was determined at room temperature as a function of the dark Fermi energy E F on samples with a relative dopant concentration range between Ϸ3ϫ10 Ϫ5 and Ϸ10 Ϫ2. A decrease of is observed with the increase of the Ga concentration until a minimum is reached for compensated samples ͑E F close to midgap level͒, where is about 16 times lower than the value obtained for intrinsic samples. This behavior is followed by an increase as E F crosses the midgap level. Then, for higher Ga doping levels, decreases again. For In-doped samples, on the other hand, a monotonic decrease of is measured for all the impurity concentration range. These results are consistent with a model which assumes that the dangling bond is the main recombination path, and give independent evidence for the lack of correlation between the defect density and E F in p-type doped a-Ge:H.

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“…The final test for an electronic semiconductor is the possibility of making good devices in a reproducible way. Solar cells (p-i-n) of relatively low conversion efficiency having an active layer of a-Ge : H have been reported [20]. It is not clear, however, whether the low conversion efficiency originates from a non-optimized device structure or active layer quality, or from a severe limitation of a-Ge : H of a more fundamental nature.…”

Section: A-ge : H Devicesmentioning

confidence: 99%

The Perspectives of Hydrogenated Amorphous Germanium as an Electronic Material

Chambouleyron

Graeff

Zanatta

et al. 1995

Physica Status Solidi (b)

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This paper refers to the perspectives of the use of hydrogenated amorphous germanium and its alloys (deposited by the rf sputtering method). It is shown that considerable progress has been made in the optimization of a-Ge: H films. The deposition conditions leading to a good quality material and the corresponding properties are discussed. The problem of material stability, as well as recent progress in the understanding of the n-and p-type doping mechanisms in the a-Ge : H network are presented.

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Electron and hole μτ products of slightly doped a-Ge:H films

Cited by 18 publications

References 5 publications

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

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

Steady-state photoconductivity of gallium- and indium-doped hydrogenated amorphous germanium thin films

The Perspectives of Hydrogenated Amorphous Germanium as an Electronic Material

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