Opto‐Electrical Properties of Group IV Alloys: The Inherent Challenges of Processing Hydrogenated Germanium

Abstract

In this paper the opto-electrical nature of hydrogenated group IV alloys with optical bandgap energies ranging from 1.0 eV up to 2.3 eV are studied. The fundamental physical principles that determine the relation between the bandgap and the structural characteristics such as material density, elemental composition, void fraction and crystalline phase fraction are revealed. Next, the fundamental physical principles that determine the relation between the bandgap and electrical properties such as the dark conductivity, activation energy, and photoresponse are discussed. The unique wide range of IV valence alloys helps to understand the nature of amorphous (a-) and nanocrystalline (nc-) hydrogenated (:H) germanium films with respect to the intrinsicity, chemical stability, and photoresponse. These insights resulted in the discovery of i) a processing window that results in chemically stable Ge:H films with the lowest reported dark conductivity values down to 4.6•10 -4 (𝛀 •cm) -1 for chemical vapor deposited Ge:H films, and ii) O, C and Sn alloying approaches to improve the photoresponse and chemical stability of the a/nc-Ge:H alloys.

Infrared analysis of catalytic CO2 reduction in hydrogenated germanium

“…In previous research it was observed that the degradation behaviour of Ge:H samples is related to the material density. 12,37 The a-Ge:H-3-5 samples are therefore processed at conditions resulting in a-Ge:H films with various porosities and expected chemical stability. The results are shown in Fig.…”

The optical performance of random and periodic textured mono crystalline silicon surfaces for photovoltaic applications

“…Two sets of devices are processed; one with a high bandgap energy (E G ) a-Si absorber (a-Si(H)) with E GaÀSi (H)) ≈1.7 eV, developed in [31], and the other with a low-E G a-Si absorber (a-Si(L)), with E GaÀSi (L) ≈1.6 eV. Deposition conditions for both can be found in [32]. The difference between the a-Si(L) and a-Si(H) absorber can be observed in Figure 11A, where the absorption onset is observably shifted from about l = 730 to l = 780 nm.…”

DIrect Sunlight into CO conversion

“…An example of the ii) material structure ↔ iii) chemical stability relation is shown in Fig. 1, where the αtot, a film-thickness independent metric for chemical stability [8] based on infrared oxidation and carbisation signatures [9], is plotted as a function of the refractive index at a wavelength of 600nm (n@600nm), which can be considered a metric for the material density. Fig.…”

“…Trendlines indicating the effect of elemental compostion and porosity are referenced in text. From [8].…”