Photoconductive gain in single crystal diamond detectors

Theodor Grünwald,Matthias Schreck

doi:10.1063/5.0044649

Abstract

Diamond crystals equipped with two metal electrodes can be operated as solid state ionization chambers for the detection of energetic radiation. Under irradiation with single α particles, the generated free electrons and holes are collected with a maximum efficiency close to 100%. When the same detectors are used for dosimetry in high intensity and high energy photon or particle beams, photoconductive gain G with values up to ≈106 is frequently observed as described in the literature. In this work, we studied theoretically the irradiation induced conductivity of perfect diamond single crystals with ohmic contacts containing nitrogen and boron with concentrations NN and NB, respectively, as only chemical impurities. Based on four rate equations, two considering the charge states of N and B and two the concentrations of free carriers n and p, and, additionally, the neutrality condition, we could derive analytical solutions for the gain G as a function of impurity concentrations, crystal thickness, and excitation density. It turned out that G varies systematically with the compensation ratio R=(NN−NB)/NB over five orders of magnitude. For R≈103, the gain G is close to unity. With decreasing R, the gain increases ∝1/R until saturation is reached for R≪1 and G≈104–105. Our theoretical data yield plausible explanations for the major trends that have been found experimentally in previous studies. They provide a valuable guideline for the future synthesis of diamond crystals to be used for manufacturing UV and radiation detectors.

Highlights

Diamond is a material with extraordinary physical properties that form the base for a wide range of potential applications1 in mechanics, optics, and electronics
When the same detectors are used for dosimetry in high intensity and high energy photon or particle beams, photoconductive gain G with values up to % 106 is frequently observed as described in the literature
It assumed a detector operated as solid state ionization chamber equipped with ohmic contacts for holes at low and moderate electric fields

Summary

Introduction

Diamond is a material with extraordinary physical properties that form the base for a wide range of potential applications in mechanics, optics, and electronics. Α particles with a kinetic energy of % 5:5 MeV continuously lose their energy until they are stopped at a depth of % 14 μm below the surface Along their trajectory, they generate electron–hole (e–h) pairs. From the transient current (TC) signal, the energy of the α-particle can be determined provided that spectroscopic grade single crystals with a charge collection efficiency (CCE) of virtually 100% are used and the average e–h pair creation energy εDia is known. In all these measurements, whether ohmic contacts like TiPtAu or Schottky-type contacts like aluminum are applied, the charge collection properties are essentially identical and the CCE values are generally 1.4

Results

Discussion

Conclusion