We began planning and writing this book in thc late 1970$ at thc ugge s stion of Manuel Cardona and Helmut Latsch. We also received considerable eo- couragement and stimulation from colleagues. Same said there was a need for instructional material in tbis area while others emphasized thc utility of a research text. We tried to strike a compromise. Thc figures, tables, and rcferences are included to enable researchcrs to obt81o quickly essential information in this area of semiconductor research. For instructoTS and stu- dents, we attempt to cover same basic ideas abaut electronic structure...