# Why n+ contact of p type Ge is 700um thick compared to p+ contact of n type Ge only 0.3um?

Whether the reason is as follows? Predominantly HPGe is p type. So compensation of large p type impurity requires more n+ contact. (700um) But n type Ge is made by doping of excess addition of n type impurity in p type HPGe. So n type impurity addition always slightly excess of p type impurity. Hence, slight excess n type impurity in n type HPGe requires, p+ contact with very less thickness. (0.3um)

• Because the n-type region is diffused lithium, and the p-type region is implanted boron. Under reverse bias the depletion region grows dramatically into the n-type region, resulting in a large detection volume. – Jon Custer Feb 4 at 14:34
• If the p contact is doped much higher than the n side, then the depletion layer will grow much further into the n region. So, if the p is, say, $10^{18}$ and the n is $10^{15}$, then the n side of the depletion layer is 1000 times wider than the p side. – Jon Custer Feb 4 at 15:45
• Lithium is used in silicon and germanium detectors since its diffusion can be driven by biasing the device. There is no way (within reason) that one could diffuse a more normal dopant (B, P, As) over 100's of microns. But with lithium one can get a nice, even doping profile at fairly low levels across millimeters to centimeters. Now, add a highly doped, ion-implanted p++ contact, and you have a great volumetric sensor. Remember, the goal is to make as wide a depletion layer as you can to increase the active volume. – Jon Custer Feb 4 at 19:54
• You seem to believe that I exist to answer your question - that is pretty annoying. Look, I've given you plenty of information above about just how gamma detectors work, why you want a thick, lightly doped region to get maximum performance, and why lithium ends up being the dopant of choice. How much clearer do I need to be? – Jon Custer Feb 5 at 17:43
• Start with physicstoday.scitation.org/doi/10.1063/1.3037792, then go look at Ortec and Canberra product literature for their detectors. – Jon Custer Feb 12 at 14:14