Trap states near the surface in (Cd,Mn)Te crystals

• Main Authors: Mycielski, A., Kochanowska, D. M., Wardak, A., Goscinski, K., Dobrowolski, W., Gorska, M., Dopierala, M., Gdanski, J., Kochanski, M., Marciniak, A.
• Format: Conference Proceeding
• Language: English
• Subjects: Anodes; Current measurement; Electric fields; Electron traps; Light emitting diodes; Surface fitting; Surface waves
• ISSN: 2577-0829
• DOI: 10.1109/NSSMICRTSD49126.2023.10338404

Laser-induced transient current technique (L-TCT) and photocurrent-voltage characteristics (PC-V) are commonly used in many laboratories to measure the values of μ e τ e and τ e . For both techniques (PC-V and L-TCT), we observed a significant impact of the surface preparation method for the contacts on the obtained results. Different contact shapes were used on the anode to increase the interaction of light-generated charge at the cathode with near-surface trap states and near-surface recombination, while a planar cathode was point-illuminated. In one experiment, the charge (electrons) generated at the cathode flowed directly to the pixel located vis a vis on the anode, while in another experiment, the charge had to flow first through the near-surface layer at the cathode and then to the lateral pixel on the anode. In the PC-V method, LEDs with photon energy ħω≤E g or ħω>E g (E g is the bandgap energy) were used as the light source with adjustable light intensity. In the L-TCT method, both contacts (on the cathode and anode) were in the form of pixels. In the L-TCT method, the laser radiation energy ħω was about 2E g . In some experiments the cathode was additionally illuminated by using LED, with ħω>E g or ħω≤E g , in other not. By using the PC-V method for the well prepared surface we obtained μ e τ e ~ 10 −3 cm 2 V −1 from fitting with the Hecht formula. For a poorly prepared surface, the results were fitted with the Ridzonova formula. The electron mobility μ e was obtained from the L-TCT method. The observed results for current waveforms in the L-TCT measurements for unilluminated and LED-illuminated cathodes with different electric fields and light intensity of LEDs were compared with the PC-V results, particularly for ħω of LED≳E g . In our interpretation we consider two processes: ionization of traps by the electric field, and deionization of traps by recombination with electrons excited by the LED light illuminating the cathode.