Photoemission Studies of Amorphous Silicon/Germanium Heterojunctions

1985 ◽  
Vol 49 ◽  
Author(s):  
F. Evangelisti ◽  
S. Modesti ◽  
F. Boscherini ◽  
P. Fiorini ◽  
C. Quaresima ◽  
...  

AbstractThe heterostructures obtained by growing a-Ge on a-Si:H and a-Si have been investigated by synchrotron radiation photoemission. We measured valence band and core level spectra on the heterostructures grown in situ under ultrahigh-vacuum conditions. A step-by-step monitoring of possible band-bending changes during the interface formation enabled us to determine unambiguously the band discontinuities. The measured values of the valence band discontinuity were 0.2 ± 0.1 eV for a-Si:H/a-Ge and 0.0 ± 0.1 eV for a-Si/a-Ge, respectively. Evidence was found for the formation of abrupt interfaces without interdiffusion.

2007 ◽  
Vol 989 ◽  
Author(s):  
Shouvik Datta ◽  
J. David Cohen ◽  
Yueqin Xu ◽  
A. H. Mahan ◽  
Howard M. Branz

AbstractWe report the effects of intentionally introducing up to ∼ 5×1020/cm3 oxygen impurities into hydrogenated amorphous silicon-germanium alloys (of roughly 30at.% Ge) grown by the hot-wire chemical vapor deposition (HWCVD) method. Deep defect densities determined by drive-level capacitance profiling (DLCP) indicated a modest increase with increasing oxygen content (up to a factor of 3 at the highest oxygen level). Transient photocapacitance (TPC) spectra indicated a clear spectral signature for an optical transition between the valence band and an additional defect level which is attributed to oxygen impurities. The oxygen impurity related defect transition has an optical threshold around 1.4eV above the valence band and also results in a negative contribution to the TPC signal. This initially led us to believe that the bandtail for the higher oxygen samples was much narrower than it actually is. Surprisingly, this additional oxygen related defect level appears to have only a very minor effect upon the estimated minority carrier collection fraction. The effects of light-induced degradation upon some of these oxygen contaminated samples were also examined. We infer the existence of a significant thermal barrier to explain the observed spectral signatures of this oxygen impurity defect.


2003 ◽  
Vol 762 ◽  
Author(s):  
J. David Cohen

AbstractThis paper first briefly reviews a few of the early studies that established some of the salient features of light-induced degradation in a-Si,Ge:H. In particular, I discuss the fact that both Si and Ge metastable dangling bonds are involved. I then review some of the recent studies carried out by members of my laboratory concerning the details of degradation in the low Ge fraction alloys utilizing the modulated photocurrent method to monitor the individual changes in the Si and Ge deep defects. By relating the metastable creation and annealing behavior of these two types of defects, new insights into the fundamental properties of metastable defects have been obtained for amorphous silicon materials in general. I will conclude with a brief discussion of the microscopic mechanisms that may be responsible.


1990 ◽  
Vol 192 ◽  
Author(s):  
Hideki Matsumura ◽  
Masaaki Yamaguchi ◽  
Kazuo Morigaki

ABSTRACTHydrogenated amorphous silicon-germanium (a-SiGe:H) films are prepared by the catalytic chemical vapor deposition (Cat-CVD) method using a SiH4, GeH4 and H4 gas mixture. Properties of the films are investigated by the photo-thermal deflection spectroscopy (PDS) and electron spin resonance (ESR) measurements, in addition to the photo-conductive and structural studies. It is found that the characteristic energy of Urbach tail, ESR spin density and other photo-conductive properties of Cat-CVD a-SiGe:H films with optical band gaps around 1.45 eV are almost equivalent to those of the device quality glow discharge hydrogenated amorphous silicon (a-Si:H).


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