High effective gummel number of CVD boron layers in ultrashallow p ⁺n diode configurations

Deposited boron layers fabricated by exposing silicon to diborane (B ₂H₆) gas in an atmospheric-pressure chemical vapor deposition reactor are investigated with respect to their electrical properties. At the applied temperatures from 500 °C to 700 °C, the deposition forms a nanometer-thick layer stack of amorphous boron (α-B) and boronsilicon compound (B_xSi_y), whereas the crystalline Si substrate is p-doped to depths below 10 nm, depending on the temperature and exposure time. The as-deposited layers can be used to fabricate high-quality p⁺n diodes with low series resistance and low saturation current values that are comparable with those of conventional deep p⁺ junctions. By investigating p-n-p structures with p⁺ B-deposited emitters, it is shown that the presence of the α-B layer increases the effective Gummel number of the diffused emitter up to about a factor of 60. The α-B layer is also demonstrated to be a stable and controllable supply of B for the formation of deep p-type regions by thermal drive-in.