We analyzed the influence of parameters of deep levels in the bulk and conditions on the surface on transient charge responses of semi-insulating samples (CdTe and GaAs). We studied the dependence on the applied bias step used for the experimental evaluation of resistivity in contactless measurement setups. We used simulations based on simultaneous solutions of 1D drift diffusion and Poisson's equations as the main investigation tool. We found out that the resistivity can be reliably determined by the transient contactless method in materials with a large density of deep levels in the bulk (e.g., semi-insulating GaAs) when the response curve is described by a single exponential. In contrast, the materials with the low deep-level density, like semiconductor radiation detector materials (e.g., CdTe, CdZnTe, etc.), usually exhibit a complex response to applied bias, depending on the surface conditions. We show that a single exponential fit does not represent the true relaxation time and resistivity, in this case. A two-exponential fit can be used for a rough estimate of bulk material resistivity only in a limit of low-applied bias, when the response curve approaches a single-exponential shape. A decreasing of the bias leads to a substantially improved agreement between the evaluated and true relaxation time, which is also consistent with the approaching of the relaxation curve to the single-exponential shape.

Faculty of Mathematics and Physics Institute of Physics Charles University Ke Karlovu 5 CZ 121 16 Prague 2 Czech Republic

Zobrazit více v PubMed

Stibal R. Contactless evaluation of semi-insulating GaAs wafer resistivity using the time-dependent charge measurement. Semicond. Sci. Technol. 1991;6:995–1001. doi: 10.1088/0268-1242/6/10/008. DOI

Seidl A., Mosel F., Friedrich J., Kretzer U., Müller G. Optical cross-sections and distribution of Fe2+ and Fe3+ in semi-insulating liquid encapsulated Czochralski grown InP: Fe. Mater. Sci. Eng. B. 1993;21:321–324. doi: 10.1016/0921-5107(93)90377-Y. DOI

Fornari R., Görög T., Jimenez J., de La Puente E., Avella M., Grant I., Brozel M., Nicholls M. Uniformity of semi-insulating InP wafers obtained by Fe diffusion. J. Appl. Phys. 2000;88:5225–5229. doi: 10.1063/1.1315327. DOI

Rasp M., Straubinger T.L., Schmitt E., Bickermann M., Reshanov S., Sadowski H. Silicon Carbide and Related Materials (Materials Science Forum 433-4) Trans Tech Publications Ltd.; Zurich, Switzerland: 2002. pp. 55–58.

Eiche C., Joerger W., Fiederle M., Ebling D., Salk M., Schwarz R., Benz K.W. Characterization of CdTe: Cl crystals grown under microgravity conditions by time dependent charge measurements (TDCM) J. Cryst. Growth. 1996;166:245–250. doi: 10.1016/0022-0248(96)00071-1. DOI

Zázvorka J., Franc J., Moravec P., Jesenská E., Šedivý L., Ulrych J., Mašek K. Contactless resistivity and photoconductivity correlation to surface preparation of CdZnTe. Appl. Surf. Sci. 2014;315:144–148. doi: 10.1016/j.apsusc.2014.07.104. DOI

Kumar S.G., Rao K.S.R.K. Physics and chemistry of CdTe/CdS thin film heterojunction photovoltaic devices: Fundamental and critical aspects. Energy Environ. Sci. 2014;7:45–102. doi: 10.1039/C3EE41981A. DOI

Rong Z., Guo X., Lian S., Liu S., Qin D., Mo Y., Xu W., Wu H., Zhao H., Hou L. Interface engineering for both cathode and anode enables low–cost highly efficient solution–processed CdTe nanocrystal solar cells. Adv. Funct. Mater. 2019;42:1904018. doi: 10.1002/adfm.201904018. DOI

Guo X., Tan Q., Liu S., Qin D., Mo Y., Hou L., Liu A., Wu H., Ma Y. High-efficiency solution-processed CdTe nanocrystal solar cells incorporating a novel crosslinkable conjugated polymer as the hole transport layer. Nano Energy. 2018;46:150–157. doi: 10.1016/j.nanoen.2018.01.048. DOI

Kuciauskas D., Kanevce A., Dippo P., Seyedmohammadi S., Malik R. Minority-carrier lifetime and surface recombination velocity in single-crystal CdTe. IEEE J. Photovolt. 2015;5:366–371. doi: 10.1109/JPHOTOV.2014.2359738. DOI

Toušek J., Kindl D., Toušková J., Dolhov S., Poruba A. Diffusion length in CdTe by measurement of photovoltage spectra in CdS/CdTe solar cells. J. Appl. Phys. 2001;89:460–465. doi: 10.1063/1.1332418. DOI

Seeger K. Semiconductor Physics. 8th ed. Springer; Berlin/Heidelberg, Germany: 2002. p. 152.

Schroder D.K. Carrier lifetimes in silicon. IEEE Trans. Electron Devices. 1997;44:160–170. doi: 10.1109/16.554806. DOI

Shockley W., Read T.W. Statistics of the recombinations of holes and electrons. Phys. Rev. 1952;87:835–842. doi: 10.1103/PhysRev.87.835. DOI

Grill R., Belas E., Franc J., Bugár M., Uxa Š., Moravec P., Höschl P. Polarization study of defect structure of CdTe radiation detectors. IEEE Trans. Nucl. Sci. 2011;58:3172–3181. doi: 10.1109/TNS.2011.2165730. DOI

Turkevych I., Grill R., Franc J., Belas E., Höschl P., Moravec P. High-temperature electron and hole mobility in CdTe. Semicond. Sci. Technol. 2002;17:1064–1066. doi: 10.1088/0268-1242/17/10/305. DOI

Yu A.Y.C. Electron tunneling and contact resistance of metal-silicon contact barriers. Solid State Electron. 1970;13:239–247. doi: 10.1016/0038-1101(70)90056-0. DOI

Sze S.M. Physics of Semiconductor Devices. 2nd ed. Wiley & Sons; Hoboken, NJ, USA: 1981. Chapter 5.

Franc J., James R.B., Grill R., Dědič V., Belas E., Praus P., Prekas G., Sellin P.J. Influence of contacts on electric field in an Au/(CdZn)Te/Au detector: A simulation. IEEE Trans. Nucl. Sci. 2010;57:2349–2358. doi: 10.1109/TNS.2010.2053049. DOI

Castaldini A., Cavallini A., Fraboni B., Fernandez P., Piqueras J. Deep energy levels in CdTe and CdZnTe. J. Appl. Phys. 1998;83:2121–2126. doi: 10.1063/1.366946. DOI