Ionization rates in 〈111〉 and 〈100〉 germanium are determined experimentally. The ionization rates obtained are expressed as α=2.72×106 exp(−1.1×106/E), β=1.72×106 exp(−9.37×105/E) for 〈111〉 and α=8.04×106 exp(−1.4×106/E), β=6.39×106 exp(−1.27×106 /E) cm−1 for 〈100〉 where α and β are ionization rates for electrons and holes, respectively, and E is the electric field. Hole- to electron-ionization-rate ratios of 〈100〉 Ge are found to be greater than those of 〈111〉 Ge. The multiplication noise power of Ge avalanche photodiodes calculated by using the ionization rates obtained shows good agreement with experimental results.
An H3PO4–H2O2–H2O solution is studied for possible use in the etching of germanium. The solution can be roughly classified into two ternary regions according to its etching characteristics: a (with a low H2O2 concentration) and b (with a high H2O2 concentration). Solutions in region b provide reproducible smooth and uniform surfaces. This solution can be used with SiO2 films and photoresists as a preferential etching mask material without dissolution or separation. It is suitable for processing germanium devices.
Ionization rates in GaAs are determined from the measurement of photocarrier multiplication. Pure electron and hole initiations are achieved by using the novel crater mesa structure and appropriate optical-injection wavelengths. The ionization rates for holes are greater than that for electrons except at highest fields. This agrees with the studies of Stillman et al., except for the individual values. The ionization rates for electrons and holes are expressed as α=5.6×106 exp(−2.41×106/E) and β=1.5×106 exp(−1.57×106/E), respectively.
Low noise avalanche photodiodes, which have an n+-p-π-p+ structure, are reported. Channeled boron ions (800 keV) in the 〈110〉 of Si are used for forming the p layer. The characteristics of this diode are compared with those fabricated by 800-keV random implantation. Low excess noise factors F=4–5 at a gain of 100 are obtained by using 〈110〉 channeled implantation, whereas F=6–7 for random implantation. By using parallel implantation, the uniformity of channeled distributions of boron ions are found to be fairly good at different locations in a wafer.
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