High Power Needs for Commercial Satellites
This overview paper presents estimates of the photovoltaic power systems needed on commercial communications spacecraft in the year 2000. These are developed in the form of power requirements based on extrapolation of the historical growth in communications traffic and are about 5 to 15 kW. The paper also addresses the key technology drivers in these photovoltaic systems. The importance of reducing mass in the power system is described in terms of the tradeoff with communications systems mass to maximize communications revenue. It surveys solar array components and subsystems to meet these future requirements and attempts to identify the development candidates with a large payoff potential and a high probability of successful development.
Recent advances in LPE GaAs-based solar cells
Several modifications were made to an infinite solution liquid phase epitaxy system that help fabricate both GaAs-based cells and thin cells that effectively reduce power-to-weight ratio for space applications. The most important development is the multiwell crucible for multilayer growth. Using a split crucible in one system, as many as five layers were grown in succession with varying Al levels and dopants. The structures grown were used to produce thin GaAs cells only 10 to 20 microns thick and also to grow cascade cell components. Results of these studies are presented and their applications to the future development of GaAs-based cells are discussed.
Study of Li-O Interaction in Si by Ion Drift
Ion drift in a reverse‐biased n‐p junction has been used to measure effective drift mobilities of Li+ between 20°–125°C in Si samples containing oxygen concentrations up to 1.3×1018 atoms/cm3. Previous experiments have indicated that under such conditions, the Li+ and oxygen will combine to form a complex of the form LiO+. The ratio of the effective drift mobility of Li+ in such samples to the known drift mobility of free Li+, when measured as a function of temperature, can be used to determine the dissociation constant of LiO+. Thus, at an oxygen concentration of 1.3×1018 atoms/cm, the diffusion constant at 50°C is reduced from 1.7×10−13 cm2/sec to (7.6±2.2)×10−16 cm2/sec by the Li+–O interaction. From this and measurements at other temperatures, the dissociation constant of LiO+ can be calculated, yielding C=(5.8×1015)±30% at 50°C with an activation energy of 0.42±0.03 ev, or more generally, C=(0.5–8.5)×1022 exp−[(0.42±0.03)e/kT]. At high concentrations the effective drift mobility is found to be invers...