Recombination In Depletion Layer Research Articles

Relative carrier densities and trap effects on the properties of CdS/CdTe

It is shown that the open-circuit voltage of CdS/CdTe heterojunction solar cells is a maximum when the carrier densities in the CdS and CdTe are approximately equal, because of the effects of a level lying 0.45 eV below the conduction band in CdTe on the junction transport. Cells investigated include those prepared by vacuum evaporation of CdS on thin-film CdTe, deposited by hot-wall vacuum evaporation on graphite substrates and on single-crystal p-CdTe:P substrates, and on single-crystal p-CdTe:P substrates. The existence of a level in the CdTe lying 0.45 eV below the conduction band is identified by measurements of the extrinsic photoresponse of CdS/CdTe junctions, and a model using this level defining junction transport is consistent with the dark and light current versus voltage relationships observed. This model involves two recombination paths: (1) depletion-layer recombination in the CdTe through the 0.45-eV level, which dominates when the electron density in the CdS in much larger than the hole density in the CdTe, and (2) tunneling of electrons from the CdS conduction band to the 0.45-eV level in the CdTe, followed by recombination, which dominates in other cases.

The Recombination of Photogenerated Minority Carriers in the Depletion Layer of Semiconductor Electrodes

The problem of depletion layer recombination in illuminated semiconductor electrolyte systems, as used for solar energy conversion, is considered. It is shown that there can be four different kinetic cases. The conditions for the existence of these different cases as a function of the potential drop across the depletion layer, the irradiance, and the photocurrent are derived. Analytical solutions for current voltage curves for the different cases are derived and criteria for distinguishing between the different cases are given. The effects of concentration polarization of the majority carriers are considered and shown to be negligible for typical semiconductors.

A flux analysis of the current–voltage characteristics of thin film frontwall illuminated and backwall illuminated liquid junction and metal junction solar cells

The flux method was used to derive analytical expressions for the photocurrent–voltage characteristics of thin film frontwall and backwall illuminated liquid junction solar cells as functions of film thickness. Expressions for these types of cells were derived without assuming the depletion layer was a minority carrier sink but with inclusion of the effects of depletion and bulk recombination, reflection, and restricted transmission at the semiconductor junction and reflection at the back contact. The effects of film thickness, donor concentration, and of partial reflection and imperfect transmission at the depletion layer/bulk layer boundary are examined. The results from this flux method are qualitatively similar to those obtained previously from different starting equations in the cases where both treatments are applicable, lending support to both approaches. In particular, the short circuit current is shown to be significantly reduced by depletion layer recombination, and by slow charge transfer when depletion layer recombination is not negligible.

An analysis of the current-voltage characteristics of thin film front wall illuminated and back wall illuminated liquid junction and schottky barrier solar cells

Analytical expressions for the current-voltage characteristics of thin film front illuminated and back illuminated liquid junc tion solar cells have been derived as a function of film thickness. The usual assumptions of a flat minority carrier quasi Fermi level across the semiconductor depletion region or a constant minority carrier concentration at the semiconductor surface have not been made. Depletion layer recombination is included in both expressions. The effects of various parameters, including thickness and back recombination velocity, are determined for both types of devices.

Effect of interface recombination at AlxGa1−xAs p–n junction perimeters on photoluminescence and current

The interfaces forming the perimeters of AlxGa1−xAs p–n junctions, such as cleaved surfaces or etched surfaces are regions of intense nonradiative recombination. Almost all of the p–n junction 2kT current is due to recombination at these nonradiative perimeters. When an uncontacted sample is studied in photoluminescence, these interfaces produce broad nonradiative regions known as large dark spots. The rate of interface recombination can be quantitatively evaluated from measurement of either the 2kT current or the large dark spot line shape. The 2kT current is usually explained in terms of the Sah, Noyce, and Shockley model of p–n depletion layer recombination. We develop an alternative model in which we show that recombination at a depleted surface will have 2kT charater. The rate of surface recombination is R=s0(np)1/2=s0ni exp(eV/2kT) where s0?4×105 cm s−1 for x=0.08 active layers with etched surfaces. This form of the recombination rate follows naturally from the requirement that the interface remain neutral.

Theory of depletion-layer recombination in silicon p–n junctions

A new theory of depletion-layer recombination in silicon p-n junctions is presented, based on the recombination statistics of 3-charge-state centres. It is shown that, with an appropriate choice of recombination-centre parameters, the forward current/voltage characteristics predicted by the theory show voltage-independent m values of ≈ 1.5.

On the wide-range bias dependence of transistor d.c. and small-signal current gain factors

A critical reappraisal is made of the bias dependence of the d.c. and small-signal a.c. current gain factors of planar bipolar transistors over a wide range of currents. This is based on a straightforward consideration of the three basic components of the d.c. base current arising due to emitter-to-base injected minority carrier transport, base-to-emitter carrier injection, and emitter-base surface depletion layer recombination effects. Among other important results it is shown that over a useful bias range the d.c. and small-signal current gain factors, respectively, obey the simple relationships: H FE∞ I c 1 3 and h fe≈ 1.5h FE Experimental results on representative n- p- n and p- n- p silicon devices are given which support most of the analytical findings.