Defect levels of semi-insulating CdMnTe:In crystals

Abstract

Using photoluminescence (PL) and current deep-level transient spectroscopy (I-DLTS), we investigated the electronic defects of indium-doped detector-grade CdMnTe:In (CMT:In) crystals grown by the vertical Bridgman method. We similarly analyzed CdZnTe:In (CZT:In) and undoped CdMnTe (CMT) crystals grown under the amount of same level of excess Te and/or indium doping level to detail the fundamental properties of the electronic defect structure more readily. Extended defects, existing in all the samples, were revealed by synchrotron white beam x-ray diffraction topography and scanning electron microscopy. The electronic structure of CMT is very similar to that of CZT, with shallow traps, A-centers, Cd vacancies, deep levels, and Te antisites. The 1.1-eV deep level, revealed by PL in earlier studies of CZT and CdTe, were attributed to dislocation-induced defects. In our I-DLTS measurements, the 1.1-eV traps showed different activation energies with applied bias voltage and an exponential dependence on the trap-filling time, which are typical characteristics of dislocation-induced defects. We propose a new defect-trap model for indium-doped CMT crystals.

Characterisation of vapour grown CdZnTe crystals using synchrotron X-ray topography

“…X-ray topography performed in the reflection geometry is sensitive to such defects (for example see Ref. [22]), but does not yield any information upon bulk regions which is crucial knowledge in the manufacture of thick radiation detectors.…”

Annealing of indium-doped CdMnTe single crystals under Cd vapors

“…The bandgap of Cd 1 À x Mn x Te increases about 13 meV/[atomic% Mn] compared with 6.7 meV/[atomic% Zn] in Cd 1 À x Zn x Te, therefore, less Mn content is added to reach the bandgap range 1.7 eV to 2.2 eV which is required for an ideal radiation detector performance [3]. Cd 1 À x Mn x Te crystals are usually grown from melt with the Bridgman method [1][2][3][4]. However, the as-grown Cd 1 À x Mn x Te ingots are always of p-type conductivity with low resistivity in the range of 10 5 -10 6 O cm, which hindered its application in detector.…”

“…Compensation with donor dopants, such as Indium (In) and Aluminum (Al), can fill out the Cd vacancies during the crystal growth to improve the resistivity of Cd 1 À x Mn x Te. However, introducing comparable concentration of donor dopants to achieve close compensation is difficult, since the states of dopants are complex with not only isolated donors (X Cd , X¼ In, Al) but also acceptors A-centers (V Cd -X Cd , X¼ In, Al) [4] and dopant impurities have segregation effects in the ingot during the melt growth of Cd 1 À x Mn x Te [6]. Post-growth thermal annealing potentially plays an important role in improving the properties of Cd 1 À x Mn x Te.…”

Charge transport properties of CdMnTe radiation detectors

“…A very recent and promising candidate is cadmium manganese telluride (CMT) [3]. Its distinct advantages of good compositional homogeneity and a highly tunable band gap compared to CdZnTe have encouraged CMT detector developments in recent years, bringing large improvements in the performance of CMT a a high resistivity single cry tal radiation detector [4][5][6][7][8][9][10][11][12][13][14]. This work describes the growth, fabrication and characterization of indium doped CMT radiation detectors with 5 % manganese concentration (1.59 eV band gap [15]).…”