The impact of neutral impurity concentration on charge drift mobility in p-type germanium

Abstract

We reported a new result of the neutral impurity scattering of holes that has impact on the charge drift mobility in high purity p-type germanium crystals at 77 Kelvin. The charge carrier concentration, mobility and resistivity are measured by Hall Effect system at 77 Kelvin. We investigated the contribution to the total charge drift mobility from ionized impurity scattering, lattice scattering, and neutral impurity scattering with the best theoretical models and experimental data. Several samples with measured Hall mobility from the grown crystals are used for this investigation. With the measured Hall mobility and ionized impurity concentration as well as the theoretical models, we calculated the neutral impurity concentration by the Matthiessen's rule. As a result, the distributions of the neutral impurity concentrations with respect to the radius of the crystals are obtained. Consequently, we demonstrated that neutral impurity scattering is a significant contribution to the charge drift mobility, which has dependence on the concentration of neutral impurities in a given germanium crystal.

The impact of neutral impurity concentration on charge drift mobility in n-type germanium

“…We have reported that the neutral impurity scattering of holes has impact on the charge drift mobility in high purity p-type germanium at 77 Kelvin [1]. We have found that the total charge drift mobility in our p-type germanium crystals is dominated by both neutral impurity scattering and acoustic phonon scattering, and the neutral impurity concentration plays an important role on the charge drift mobility.…”

“…For the mobility caused by the scattering of optical phonons in germanium, µ O , it can be ignored for the same reason as we discussed in our previous work [1,24,25]. The mobility due to dislocation scattering, µ D can also be ignored since the dislocation density for n-type high purity germanium crystal is similar to that of p-type high purity germanium crystal [1,26,27].…”

“…Similar to the calculation we presented in the paper about p-type germanium crystal [1], the total charge drift mobility is impacted independently by different scattering mechanisms and can be determined using Matthiessen's rule [13]:…”

“…where µ I is in cm 2 /(V•s) and N i is in /cm 3 . The details for these two models have been discussed from Eq.2.4 to Eq.2.7 in our previous work [1]. Eq.…”

Pulse-shape calculations and applications using the AGATAGeFEM software package

“…Neither the drift model for electrons nor for holes takes into account the effects of crystal temperature or impurity concentrations on the charge-carrier drift velocities although these effects modify the drift velocities [34]. The effect of varying the hole-drift velocity was studied within the GRETINA [22] and AGATA collaborations [35].…”