Experimental studies on the temperature dependence of Germanium semiconductor detectors and on their pixilation for high spatial resolutions

半导体探测器中电子-空穴对热产生的噪声电流基本上受玻尔兹曼因子exp（-E_<th>/kT）的控制，其中E_<th>表示特征能量，kBoltmann常数，T表示绝对温度。硅半导体探测器可以在室温下工作，这是因为<e-h><10><-3>在T=25℃时，由于E_<th>（1.1eV）很高，硅中的电子空穴对密度n_（？）而锗中的n在25℃时<e-h>高达10^<13>cm^<-3>，这是由于锗的E_<th>（0.7 eV）值很低，使锗半导体探测器必须在低温条件下工作。然而，<e-h>在中等低温条件下（T=-65℃），锗中的n_i已经与室温下硅中的n_i一样低。当电极尺寸与本工作中假设的像素尺寸（100 μm × 100 μm）一样小时，噪声电流应减小到小于100 nA pe ...更多信息 R像素，因为它与每个像素电极覆盖的半导体的体积成比例。另一方面，电离粒子产生的电子-空穴对的密度数与探测体积无关，随着电离粒子能量的增加而增加，并局限于几百μm以内。这个论点表明，当像素化在几百μm时，锗半导体可以在室温附近工作。实验结果表明，在体积为1 mm × 1 mm的微型锗探测器中，室温下噪声电流已降至10 mA，在-73℃时噪声电流又降低了两个数量级。这意味着将锗晶体像素化为0.2 mm × 0.2 mm × 0.3 mm的标准尺寸，噪声电流将降低到30 nA以下，并支持像素化锗探测器在近室温下的操作可能性。然而，在高于10 V的施加电压下观察到暗电流，这可能是表面泄漏电流。因此，最新版本的像素化锗探测器的晶体体积为5 mm × 5 mm，像素尺寸为0.75 mm × 0.75 mm，像素数为2 × 2，以及用于去除暗电流的保护环电极。少

The noises current originated by thermal generation of electron-hole pairs in semiconductor detectors is basically governed by the Boltzmann factor of exp(-E_<th>/kT), where E_<th> denotes the characteristic energy, k Boltmann constant, and T the absolute temperature. Silicon semiconductor detectors can be operated at room temperature, because the number of density of electron-hole pairs, n_<e-h>, in silicon is on he order of 10^<10> cm^<-3> at T=25℃ owing to the high value of E_<th>(1.1 eV). On the contrary, n<e-h> in germanium is as high as 10^<13> cm^<-3> at T=25℃ due to the low value of E_<th>(0.7 eV), making the cryogenic condition compulsory to the operation of germanium semiconductor detectors. However, n_<e-h> in germanium at moderate cryogenic condition (T=-65℃) is already as low as that in silicon at room temperature. With an electrode as small as the pixel size assumed in the present work (100 μm × 100 μm), furthermore, the noise current should be reduced less than 100 nA pe … More r pixel, since it is proportional to the volume of the semiconductor each pixel electrode covers. The number of density of electron-hole pairs generated by ionizing particles is, on the other hand, independent from the detection volume, increases with the energy of ionization particles, and localized within a few hundreds μm. This argument suggests that, when pixilated in a few hundreds μm, the germanium semiconductor can be operated near room temperature. The present study has confirmed that the noise current is already reduced to 10 mA at room temperature in a tiny germanium detector with a volume of 1 mm × 1mm, and is further reduced by two orders of magnitude at T=-73℃. This implies that the noise current will be reduced below 30 nA with a germanium crystal pixilated into a proposed standard size of 0.2 mm × 0.2 mm × 0.3 mm, and supports the operation possibility of a pixilated germanium detector at near room temperature. However, there was a dark current observed with an applied voltage higher than 10 V, which is presumably a surface leakage current. The latest version of pixilated germanium detectors fabricated has, therefore, a crystal volume of 5 mm × 5 mm, a pixel size of 0.75 mm × 0.75 mm, and a pixel number 2 × 2, together with a guard-ring electrode that is to remove the dark current. Less