[42]. Depending on the mass of the incident particle light doses are generally considered to be less than 1 X 10E15 ions/cm2 [42]. Table III gives the typical proton doses per year and the energies associated with such proton experienced in near Earth space [41], It is apparent from the data shown in Table III that light damage is to be expected in space over a relatively short time period (<1 year). Passive solar annealing, lithium doping and quartz shielding have been means used in the past to reduce the impact of radiation damage on solar cells. For an SPS glass shielding and periodic annealing will most likely be utilized [6]. Anneals in excess of 750 C place special material constraints on the system. Silicon Processing Once the silicon crystal of the desired shape is obtained, a variety of processing steps such as doping, insulator deposition or film growth, metallization and the patterning of the aforementioned steps are performed. Dopants in the part per million to part per billion range are used to change the electrical characteristics of semiconductors. There are two types of dopants: n-type (P, As, Sb) and p-type (B, Al, Ga). Dopants are commonly introduced during crystal growth, or diffused into the silicon from a gas, by gas transport from a dopant oxide or nitride, from a spun-on source, a deposited dope oxide film, by alloying with a dopant metal (Al, Sb), or by ion implantation. If imported gases and liquids are excluded only the alloying and ion implantation techniques can be utilized in space. Alloying is one of the oldest doping techniques used in the semiconductor industry [43]. Aluminum, a common element in the lunar soil, alloys readily with silicon. Selective alloy doping can be obtained by evaporation of Al through a solid mask. Ion
RkJQdWJsaXNoZXIy MTU5NjU0Mg==