Irving Weinberg

Radiation resistance and comparative performance of ITO/InP and n/p InP homojunction solar cells

The radiation resistance of ITO/InP cells processed by DC magnetron sputtering is compared to that of standard n/p InP/GaAs homojunction cells. After 10 MeV proton irradiations, it is found that the radiation resistance of the present ITO/InP cell is comparable to that of the n/p homojunction InP cell and that both InP cell types have radiation resistances significantly greater than that of GaAs. The relatively lower radiation resistance observed at higher fluence for the InP cell with the deepest junction depth is attributed to losses in the cell emitter region. Diode parameters obtained from I/sub sc/-V/sub oc/ plots, data from surface Raman spectroscopy, and determinations of surface conductivity type are used to investigate the configuration of the ITO/InP cells. It is concluded that these latter cells are n/p homojunctions, the n-region consisting of a disordered layer at the oxide-semiconductor interface.<<ETX>>

Key factors limiting the open circuit voltage of n/sup +/pp/sup +/ indium phosphide solar cells

The problem of the presently obtained best open-circuit voltage (V/sub oc/) values of n/sup +/pp/sup +/ InP solar cells being considerably smaller than those predicted by basic theory is theoretically investigated. The values of some key parameters in the cells are obtained with a computer model by closely matching theoretical and measured curves for illuminated I-V, log I/sub sc/-V/sub oc/, and spectral response characteristics of a high-efficiency (17.9%) InP solar cell made by the Spire Corporation. An optimally designed InP solar cell with nearly the best efficiency that it is capable of providing in the n/sup +/pp/sup +/ shallow homojunction structure is described and modeled using these parameters. The performance parameters of the optimally designed solar cell are calculated, and it is shown that such a cell is capable of having an efficiency of 22.61% under 1 AM0 at 27 degrees C (300 K). Using a baseline solar cell design which is a slightly modified and improved version of the Spire 6 cell, the key factors which limit the open-circuit voltage V/sub oc/ of such a solar cell are discussed.<<ETX>>

Comparison of n/sup +/p and p/sup +/n structures in indium phosphide solar cells

The expected performances of n/sup +/p and p/sup +/n indium phosphide solar cells are compared. PC-1D, a quasi-one-dimensional computer program based on solving semiconductor transport equations by a finite-element method, was used to model n/sup +/p and p/sup +/n indium phosphide solar cell structures. The calculations show that the n/sup +/p structure offers a better short-circuit current, but that the p/sup +/n structure offers improved open-circuit voltage and overall gain in cell efficiency. The radiation resistance of p/sup +/n InP cells is compared to that of n/sup +/p cells. It is shown that the conflicting results obtained in experiments indicate the need for a systematic reevaluation of the comparative radiation resistance of the two InP cell configurations.<<ETX>>

Photoluminescence lifetime measurements in InP wafers

An apparatus that measures the minority carrier lifetime in InP is described. The technique stimulates the sample with a short pulse of light from a diode laser and measures the photoluminescence (PL) decay to extract the minority carrier lifetime. The photoluminescence lifetime in InP as a function of doping on both n- and p-type material was examined. The results show a marked difference in the lifetime on n-type InP and p-type InP of similar doping levels. N-type InP shows a lifetime considerably longer than the expected radiative limited lifetime.<<ETX>>

Modeling of low‐bandgap solar cells for thermophotovoltaic applications

Low‐bandgap solar cells can be used effectively and efficiently for thermophotovoltaic applications. A 0.75 eV bandgap InGaAs solar cell is an ideal device for the Er‐YAG selective emitter with a emission peak around 1.5 μm. Modeling results predict that the InGaAs cell efficiencies of nearly 30% are possible for the Er‐YAG selective emitter source at 1500 K.

Effective first layer antireflective coating on InP solar cells grown by chemical oxidation

Commonly used first layer antireflection (AR) coatings for InP solar cells, such as ZnS, Sb/sub 2/O/sub 3/, SiO/sub 2/ and SiO, deposited either by electron-beam or by resistive evaporation, destroy the stoichiometry of the emitter surface. Consequently, the surface recombination velocity (SRV) at the emitter surface is significantly increased, leading to a reduction in the values of solar cell performance parameters. This can be prevented by growing, after contacting, a thin native oxide layer on the emitter surface. Best results are obtained using a phosphorus-rich chemical oxide grown by chemical oxidation using a newly developed etchant (PNP) based on HNO/sub 3/, o-H/sub 3/PO/sub 4/ and H/sub 2/O/sub 2/. The chemical oxide grown on p/sup +/-InP emitters, using the PNP etchant, passivates the surface and can be used as a first layer AR coating.<<ETX>>

High voltage thermally diffused p/sup +/n solar cells

The possibility of fabricating thermally diffused p/sup +/n InP solar-cells with high open-circuit voltage without sacrificing the short circuit current is discussed. The p/sup +/n InP junctions were formed by Cd and Zn diffusion through a 3-5 nm thick anodic or chemical phosphorus-rich oxide cap layer grown on n:InP:S (with N/sub D/-N/sub A/=3.5*10/sup 16/ and 4.5*10/sup 17/ cm/sup -3/) Czochralski LEC-grown substrates. After thinning the emitter from its initial thickness of 1 to 2.5 mu m down to 0.06-0.15 mu m, the maximum efficiency was found when the emitter was 0.2 to 0.3 mu m thick. Typical AM0, 25 degrees C values of 854-860 mV were achieved for V/sub oc/, J/sub sc/ values were from 25.9 to 29.1 mA/cm/sup 2/ using only the P-rich passivating layer left after the thinning process as an antireflection coating.<<ETX>>

High quality thermally diffused p/sup +/-n InP structures

Cd diffusion and Zn diffusion into n-InP:S (N/sub D/ =3.5*10/sup 16/ and 4.5*10/sup 17/ cm/sup -3/) were performed by a closed ampoule technique at diffusion temperatures from 500 to 600 degrees C by using either high-purity Cd and Zn or Cd/sub 3/P/sub 2/ and Zn/sub 3/P/sub 2/. The Czochralski LEC grown substrates with etch pit densities (EPDs) from 3*10/sup 4/ to 7*10/sup 4/ cm/sup -2/ were used. Diffusions were performed through either bare surfaces or using SiO/sub 2/ (50-100 AA thick) and phosphorus-rich anodic and chemical oxides (25-50 AA thick) as cap layers. Specular surfaces have been obtained after Cd diffusion from Cd/sub 3/P/sub 2/ through P-rich oxide cap layers with a very low surface dislocation density which goes through a minimum of 400-800 cm/sup -2/ at the diffusion temperature of 560 degrees C. AM0 250 degrees C V/sub oc/ values as high as 860 mV from solar cells made on these structures are reported.<<ETX>>

Predicted performance of near-optimally designed indium phosphide space solar cells at high intensities and temperatures

The authors calculated the expected performance dependence of near-optimally designed shallow homojunction n/sup +/pp/sup +/ InP solar cells on incident intensities up to 200 AMO and temperatures up to 100 degrees C (373 K). Both circular and rectangular cells were considered, the former for use in a Cassegrainian concentrator array at 100 AM0, 80-100 degrees C and the latter for use in a Slats concentrator array at 20 AM0, 80-100 degrees C. With efficiencies near 22% at 80 degrees C, both the circular and rectangular InP shallow homojunction solar cells compare very favorably to GaAs cells of the same design and may be preferable to the GaAs cells for space applications because of the superior radiation tolerance of the InP cells.<<ETX>>

Experiment-based projected high efficiency thermally diffused p/sup +/n (Cd,S) InP solar cells for space applications

By drastically reducing the defect densities of p/sup +/n (Cd,S) InP diffused structures the authors have succeeded in fabricating p/sup +/n InP solar cells with measured AM0, 25/spl deg/C V/sub /spl prop// values exceeding 880 mV, without anti-reflection (AR) coating. Experiment-based projected maximum achievable AM0, 25/spl deg/C efficiency of these cells is 21.3%. Preliminary investigation of the performance parameters of p/sup +/n (Cd,S) InP structures and solar cells after irradiation with 10/sup 13/ cm/sup -2/ 3MeV protons indicate higher radiation tolerance of this configuration as compared to n/sup +/p InP configuration due to its better annealing properties.<<ETX>>