InP shallow-homojunction solar cells

Indium phosphide solar cells with very thin n-type emitters have been made by both ion implantation and metalorganic chemical vapor deposition. Air mass zero efficiencies as high as 18.8 percent (NASA measurement) have been achieved. Although calculations show that, as is the case with GaAs, a heterostructure is expected to be required for the highest efficiencies attainable, the material properties of InP give the shallow-homojunction structure a greater potential than in the case of GaAs. The best cells, which were those made by ion implantation, show open-circuit voltage (V sub oc) of 873 mV, short-circuit current of 357 A/sq m (35.7 mA/sq cm), and fill factor of 0.829. Improvements are anticipated in all three of these parameters. Internal quantum efficiency peaks at over 90 percent in the red end of the spectrum, but drops to 54 percent in the blue end. Other cells have achieved 74 percent in the blue end. Detailed modeling of the data indicates that a high front surface recombination velocity is responsible for the low blue response, that the carrier lifetime is high enough to allow good carrier collection from both the base and the emitter, and that the voltage is base-limited

High efficiency GaAs-Ge tandem solar cells grown by MOCVD

High conversion efficiency and low weight are obviously desirable for solar cells intended for space applications. One promising structure is GaAs on Ge. The advantages of using Ge wafers as substrates include the following: they offer high efficiency by forming a two-junction tandem cell; low weight combined with superior strength allows usage of thin (3 mil) wafers; and they are a good substrate for GaAs, being lattice matched, thermal expansion matched, and available as large-area wafers

SUBGOVERNMENTS AND THE IMPACT OF POLICY FRAGMENTATION AND ACCOMMODATION

For many years political scientists have utilized the subgovernment model of policy-making to explain certain types of policy output. Recently a number of scholars have argued that the traditional conceptualization of subgovernments was simplistic and incomplete. They view subgovernments as a complex and integral part of the larger policy-making environment. This paper examines this "new" subgovernment by analyzing its role in contemporary public policy-making. If subgovernments have lost their autonomy and been exposed to the complex demands of the larger political system, what impact does this have on policy outputs? Relying upon the literature on subgovernments and their principal components, the paper offers an interpretation of how subgovernments have potentially expanded their influence on public policy as a result of two contemporary developments: policy-making fragmentation, and the accommodation of policy outputs. Copyright 1988 by The Policy Studies Organization.