Development of Lithium-Drifted Silicon Detectors Using an Automatic Lithium-Ion Drift Apparatus

Abstract

Using a computer-controlled drift apparatus, we have developed lithium-ion drift techniques to produce large-size silicon detectors with a high success rate. Based on the improved techniques, we have made detectors with a 115×25×2 mm3 sensitive volume. The variation of the detector sensitivity has been shown to be homogeneous over the measurement area using 1150 nm infrared light.

Developing a mass-production model of large-area Si(Li) detectors with high operating temperatures

“…There is also one report indicating that it is empirically preferable for Li drift [22]. Resistivity of ∼1000 Ω · cm corresponds to an acceptor concentration of N A ≈ 10 13 atoms/cm 3 [19], which is an order of magnitude lower density than that used in some of previous studies of large-area Si(Li) detectors [20][21][22][23]. Substrate with a lower p-type acceptor concentration requires fewer Li ions for compensation, thus reducing the temperature and time required in the diffusion process.…”

“…Several studies have reported that uniformly drifting Li ions into a thick, large-area, p-type Si wafer is difficult mainly due to defects and contaminants, such as oxygen and carbon, in the Si crystal [20][21][22][23][32][33][34]. These behave as traps for Li ions and hence decrease Li ion mobility in the crystal, making it hard to uniformly drift.…”

“…These behave as traps for Li ions and hence decrease Li ion mobility in the crystal, making it hard to uniformly drift. Previous works also demonstrate that these impurities and defects concentrate especially in the central region of Si wafer, resulting in an uncompensated region at the center of the wafer's p-side after the Li drift [21][22][23].…”

“…Indeed, our heating temperature and time during the diffusion are cooler and shorter than previous research on large-area Si(Li) using ∼100 Ω · cm crystal. For example, [20] and [21] maintained the wafer at 400 • C for 15 min to form a >100 µm diffused layer. Reference [22] requires the wafer to be maintained at a temperature ranging 300 • C to 400 • C for 5−20 min to obtain a diffused depth of 100−200 µm.…”

“…However, all of these EDX Si(Li) detectors are small with a diameter of ∼1 cm, and operated mainly at liquid nitrogen temperature, which is significantly lower than that required for GAPS. Several previous studies have reported on large-area Si(Li) detectors [20][21][22]; however, all these methods required removing the un-drifted region after the Li drift, because achieving a uniform drift across a large-area was impossible. As an approach to address this difficulty, it was demonstrated that uniform Li-drifting can be conducted into a large-area Si wafer by drifting towards a boron-implanted p-side layer [23][24][25][26][27].…”