436 BELL SYSTEM TECHNICAL JOURNAL 



of ordinary rectifying junctions because, on both sides of the junction, 

 both electron flow and hole flow must be considered. In fact, a major 

 portion of the hole current may persist into the w-type region and vice- 

 versa. In later sections we show how this feature has a number of inter- 

 esting consequences, which we shall describe briefly in this introduction. 



A p-n junction may act as an emitter in the transistor sense, since it can 

 inject hole current into n-type material. The a-c. impedance of a p-n junc- 

 tion may exhibit a frequency dependence characterized by this diffusion 

 of holes and of electrons. For high frequencies the admittance varies ap- 

 proximately as {iuy^ and has comparable real and imaginary parts. When 

 a p-n junction makes contact to a piece of «-type material containing a high 

 concentration of injected holes, it acts like a semipermeable membrane and 

 tends to come to a potential which corresponds to the hole concentration. 



Although some results can be derived which are valid for all p-n junctions, 

 the diversity of possible situations is so great and the solution of the equa- 

 tions so involved that it is necessary to illustrate them by using a number 

 of special cases as examples. In general we shall consider cases in which the 

 semiconductor may be classified into three parts, as shown in Fig. 1. The 

 meaning of the transition region will become clearer in later sections; in 

 general it extends far enough to either side of the point at which Nd — Na = 

 so that the value of ] A^d — Na \ at its boundaries is not much smaller than 

 in the low resistance parts of the specimen. As stated above, appreciable 

 hole currents may flow into the //-region beyond the transition region. For 

 this reason, the rectification process is not restricted to the transition region 

 alone. We shall use the word junclion to include all the material near the 

 transition region in which significant contributions to the rectification 

 process occur. It has been found that various techniques may be employed 

 to make nonrectifying metallic contacts to the germanium; when this is 

 properly done, the resistance measured between the metal terminals in a 

 suitably proportioned specimen is due almost entirely to the rectifying 

 junction up to current densities of 10~^ amp/cm^. 



directed by K. Lark-Horovitz: S. Renzer, Pli\s. Rev. 72, 1267 (1947); M. Becker and 

 H. Y. Fan, Pliys. Rev. 75, 1631 (1949); and H. Y. Fan, Pliys. Rev. 75. 1631 (1949). Similar 

 junctions occur in lead sultide according to L. Sosnowski, J. Slarkiewicz and 0. Simpson, 

 Nalure 159, 818 (1947), L. Sosnowski, Pliys. Rev. 72, 641 (1947), and L. Sosnowski, B. 

 \V. Socle and J. Starkiewirz, Nalure 160. 471 (1947). The theory described here has been 

 discussed in connection wiih photoelectric effects in p-n junctions by F. S. Goucher_. 

 Meeting of the American Physical Society, Cleveland, March 10-12, 1949 and by W. 

 Shocklcy, G. L. Pearson and M. Sparks. Pliys. Rev. 76, 180 (1949). Fcr a general review 

 of ccnductivitv in p- and n-lvpe silicon see G. L. Pearson and J. Bardeen, Plivs. Rev. 75, 

 865 (1949), and I. H. Scaff.'H. C. Theucrer and F. F. Schumacher, Jl. of Metals, 185, 

 383 (1949) and W. G. Pfann and J. H. Scaff, .//. of Melals, 185, 3S9 (1949). The latter 

 two papers also discuss photo-voltaic barriers. The most recent and thorough theory for 

 frequency effects in metal semiconductor rectifiers is given elsewhere in this issue (J. 

 Bardeen, Bell Sys. Tech. Jl., July 1949). 



