摘要:

Steady state electroluminescence depends upon radiative and non‐radiative processes often governed by recombination centers. Transient space charge limited currents also depend upon capture by these same deep states although recombination is not involved. We have studied both of these phenomena as a function of photodegradation in order to gain insight into the nature of Staebler‐Wronski defects. We have found that photodegradation primarily shortens the non‐radiative lifetime but has little effect upon the radiative lifetime. On the other hand, photodegradation seems to have a profound effect upon the transient space charge limited current. We have not yet determined whether this is a junction or a bulk effect.

ISSN:0094-243X    

DOI:10.1063/1.41024

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Using low temperature above‐ and below‐gap excitation of light induced electron spin resonance (LESR) large densities (≳1017cm−3) of charged midgap states are shown to be associated with the interfaces and/or surfaces of a‐Si:H films. In all cases (films of 5, 10 and 15 &mgr;m thicknesses) the below‐gap LESR produces the same asymmetry in the intensities of the electron and hole lines as we reported earlier, and the induced spin densities scale with the number of interfaces within ±15%. When considered as bulk spin densities, the results vary by more than a factor of three.

ISSN:0094-243X    

DOI:10.1063/1.41025

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The electronic stability of a‐Si:H films deposited by different methods and a wide range of preparation parameters has been investigated by keV‐electron irradiation. Employing an electron dose of about 70 J/cm2a metastable defect density near its saturation level was created. The defect density of the initial and the irradiated state has been determined by CPM and PDS. It was found that the saturation level of the creation of metastable defects &Dgr;Nsatis independent on the previous (stable) defect density Nowithin the experimental inaccuracy. Meanwhile an evident increase of &Dgr;Nsatwith the hydrogen content CH‐fraction bonded at inner surfaces, and the optical gap was observed. Obviously, there exists a dependence of &Dgr;Nsaton the preparation temperature. The saturation behaviour of the films does not always correlate with that of pin solar cells prepared with the same i‐material.

ISSN:0094-243X    

DOI:10.1063/1.41026

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report a study of the accuracy with which the Urbach energy and defect density of a‐Si:H and a‐Si,Ge:H alloys may be extracted from optical absorption spectra determined by the constant photocurrent method. Surprisingly, a great part of the discrepancy results from evaluation of the CPM spectra, rather than from the normalization of the spectra to an absolute scale of the optical absorption coefficient. We will discuss the sources of error in several existing methods of data analysis and the adaptability of these methods for studying alloys. As well, we propose a new method of analysis, one in which we look at the excess subgap absorption over a range of energies.

ISSN:0094-243X    

DOI:10.1063/1.41027

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Constant photocurrent (CPM) and steady state photograting (SSPG) measurements have been performed on a series of hot wire (HW) and glow discharge (GD) hydrogenated amorphous silicon (a‐Si:H) films, where the substrate temperature was varied in each case to affect the bonded H content. A reduction in the magnitude of the Staebler‐Wronski effect, as observed by CPM after saturation light soaking, is seen when the H content is reduced in both sets of samples, but the lowest saturated CPM values and the highest SSPG diffusion lengths measured after saturation occur for HW films having H contents in the range 1‐4 at.%. Although correlations exist between the number of excess defects produced by saturation light soaking and microscopic parameters such as the H content and the optical bandgap, there is not a simple correspondece for both sets of samples. This suggests that the Staebler‐Wronski saturation may be influenced in part by the film microstructure.

ISSN:0094-243X    

DOI:10.1063/1.41028

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Highly stable a‐Si:H was prepared by a novel technique termed ‘‘chemical annealing’’. The light induced metastable defects were reduced dramatically in the films prepared by this method at 300 °C or higher. The structural relaxation in the vicinity of the growing surface was enhanced by the treatments with atomic hydrogen or excited noble gases, He* and Ar*.

ISSN:0094-243X    

DOI:10.1063/1.41029

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

This paper discusses the deposition of microcrystalline silicon, &mgr;c‐Si, by the remote plasma enhanced chemical vapor deposition process. We discuss the deposition process, and the properties of undoped and doped &mgr;c‐Si thin films. We emphasize the properties of an ‘‘intrinsic’’ &mgr;c‐Si thin films material that is obtained by light boron doping. The properties of this material, in particular its effective band‐gap of 1.44 eV, its relatively high photoconductivity and its undetectable Staebler‐Wronski degradation make it a candidate material for the i‐layer photo‐active constituent of p‐i‐n PV devices.

ISSN:0094-243X    

DOI:10.1063/1.41030

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The conditions for the preparation of high quality and light stable a‐Ge:H material were investigated. By ‘‘hard’’ deposition, i.e., by strong ion bombardment during the rf‐plasma deposition, it is possible to obtain a material with a photoconductivity of &eegr;&mgr;&tgr;=10−6cm2/V (at 950nm). This value does not change after 2500 hours AM1 illumination. Also a stress test under keV‐electron irradiation shows the material to be stable. By small angle X‐ray scattering this stable materials was characterized as free from small voids. Larger voids are present in both ‘‘hard’’ and ‘‘soft’’ deposited a‐Ge:H material and therefore seem not to be mainly responsible for light degradation. The high photoconductivity and the good stability are a precondition for the use of a‐Ge:H in tandem solar cells.

ISSN:0094-243X    

DOI:10.1063/1.41047

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have studied the electrical and optical properties along with light induced degradation of a‐Si:H, Cl films prepared by electron cyclotron resonance (ECR) plasma. We find that there is an irreversible decrease in dark conductivity of these films after vacuum anneal at 200°C. The degradation in photoconductivity of these films due to the Staebler‐Wronski effect is smaller than that observed in glow discharge prepared a‐Si:H films.

ISSN:0094-243X    

DOI:10.1063/1.41032

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Electron‐cyclotron‐resonance (ECR) plasma offers a potentially better way of controlling the growth chemistry of a‐Si:H. Such control can be expected to improve the microstructure of a‐Si:H, and hence its stability. In this paper, we report on the preparation and properties of a‐Si:H films produced using a remote ECR plasma at low pressures. It is shown that the ECR‐ a‐Si:H films have electronic properties comparable to glow‐discharge produced films. The stability of ECR‐films appears to be superior to glow‐discharge‐films.

ISSN:0094-243X    

DOI:10.1063/1.41033

出版商:AIP    

年代:1991

数据来源: AIP