substance: cadmium selenide (CdSe) property: hole mobility, carrier and ion diffusion Hall and drift mobilities of holes are smaller than those of electrons. hole Hall mobility (in cm 2 /Vs) 26s11d30 µ H,p 40 T = 300 K cubic CdSe/(100)GaAs, N-doped epitaxial 94O films, free-hole concentration 1 10 17 cm 3 50 T = 300 K pulsed field effect 69I 13...17 T = 300 K Hall effect 74B 10 T = 300 K Hall effect 75P 0.5 T = 300 K ion implanted layers, Hall effect 78K hole drift mobility (in cm 2 /Vs) µ dr,p 75 T = 300 K time of flight measurement 72C 3 10 3 T = 300 K high resistivity samples, time of flight 75P measurement 20 T = 300 K electron beam excited pulses 77P Dependence on electric field: Fig. 1 hole diffusion coefficient D p 65 cm 2 /s T = 13 K nonlinear transient gratings 78J D p 0.52 cm 2 /s T = 300 K surface diffusion constant, surface 85S photovoltage measurements on films exciton diffusion coefficient (in cm 2 /s) Exciton diffusion coefficients vs temperature, see Fig. 2. A review on exciton diffusion in CdSe in comparison with CdS and Cd(S,Se) has been published by [92S]. D 140 T = 2 K transient-grating measurements 93E 26 T = 30 K D 20 T = 2 K transient-grating measurements 93E 6.6 T = 30 K D x 2.5 T = 4.5 K transient-grating measurements, 92P 3.6 T = 30 K excitation below A n=2 exciton 20 T = 1.8 K transient-grating measurements, 92S 6 T = 40 K excitation below A n=1 exciton carrier diffusion lengths L [µm] n [cm 3 ] τ [ns]* T [K] remarks 13(7) 5 9 10 17 0.4(1) 5 electron-hole plasma expansion, local 85M PL intensity and gain spectra 0.32 0.43 2.05 10 16 minority-carrier diffusion, theory 87M 0.09? 80 hole diffusion length, estimated from 85P photoresponse measurements on hex-cdse heterostructures on n-gap 0.002 0.077? 300 electrodeposited films on Ti substrates 87S after different postdeposition treatments * τ carrier lifetime
exciton diffusion lengths Exciton diffusion length vs temperature, see Fig. 3. L x [µm] n [cm 3 ] T [K] remarks 0.025 0.125? 80 hex-cdse heterostructures on n-gap 85P carrier diffusion velocity (in 10 6 cm/s) Given T are bath temperatures υ sr 0.45...1.2 T = 300 K surface recombination velocity, from 85S surface photovoltage measurements on films υ ct 0.4 carrier transfer velocity at surface υ p = υ sr + υ ct 1.2...1.35 true carrier velocity at surface/interface carrier ambipolar diffusion velocity (in 10 6 cm/s) υ D 3 T = 5 K drift-υ D electron-hole plasma expansion, 85M local PL intensity and gain spectra 19 T = 4.2 K expansion velocity of the plasma-exciton 90S boundary, time-resolved absorption ion and defect diffusion and migration Self-diffusion of constituent ions Cd 2+ is described by the formula D = D 0 exp(-q/k B T). Fig. 4 gives D as function of temperature. D 0 0.058 cm 2 /s T variable Auger spectroscopy 91F Q 1.73 ev E(Se sublimation ) 1.2(1) ev T variable Se desorption experiments 98O
References: 69I Inoue, M.: J. Phys. Soc. Jpn. 26 (1969) 1186. 72C Canali, C., Nava, F., Ottaviani, G., Paorici, C.: Sol. State Commun. 11 (1972) 105. 74B Baubinas, R., Januskevicius, Z., Sakalas, A., Viscakas, J.: Solid State Commun. 15 (1974) 1731. 75P Petravichyus, A. D., Yushka, G. B., Baubinas, R. V.: Sov. Phys. Semicond. (English Transl.) 9 (1976) 1530 and Fiz. Tekh. Poluprovodn. 9 (1975) 2372. 77P Petravicyus, A., Juska, G., Smilga, A.: Sov. Phys.-Collect. (USA) (English Transl.) 18 (1977) 54 and Litov. Fiz. Sb. 17 (1977) 85. 78J Jarasiunas, K., Gerritsen, H. J.: Appl. Phys. Lett. 33 (1978) 190. 78K Kutra, J., Sakalas, A., Zindulis, A., Zuk, V.: Thin Solid Films 55 (1978) 421. 85M Majumder, F.A., Swoboda, H.-E., Kempf, K., Klingshirn, C.: Phys. Rev. B 32 (1985) 2407. 85P Polyakov, V.I., Ermakov, M.G., Perov, I., Khomich, A.V.: Sov. Phys. Solid State 27 (1985) 1784 [Fiz. Tverd. Tela 27 (1985) 2971]. 85S Storr, G.J., Haneman, D.: J. Appl. Phys. 58 (1985) 1677. 87M Morre, A.R., Lin, H.-S.: J. Appl. Phys. 61 (1987) 5366. 87S Szabo, J.P., Cocivera, M.: J. Appl. Phys. 61 (1987) 4820. 90S Sasaki, F., Masumoto, Y.: J. Phys. Soc. Jpn. 59 (1990) 1150. 91F Fedorov, V.A., Ganshin, V.A., Korkishko, Yu.N.: J. Cryst. Growth 112 (1991) 781. 92P Pantke, K.-H., N rgaard, J., Erland, J., Hvam, J.M.: J. Lumin 53 (1992) 317. 92S Schwab, H., Dörnfeld, C., Göbel, E.O., Hvam, J.M., Klingshirn, C., Kuhl, J., Lyssenko, V.G., Majumder, F.A., Noll, G., Nunnenkamp, J., Pantke, K.-H., Renner, R., Reznitsky, A., Siegner, U., Swoboda, H.E., Weber, Ch.: Phys. Status Solidi (b) 172 (1992) 479. 93E Erland, J., Razbirin, B.S., Pantke, K.-H., Lyssenko, V.G., Hvam, J.M.: Phys. Rev. B 47 (1993) 3582. 94O Ohtsuka, T., Kawamata, J., Ziqiang Zhu, Yao, T.: Appl. Phys. Lett. 65 (1994) 466. 98O Ohishi, M., Yoneta, M., Saito, H., Sawada, H., More, S.: J. Cryst. Growth 184/185 (1998) 57.
Fig. 1. CdSe. Electron and hole drift velocity of 2 different samples vs. electric field strength at room temperature [72C].
Fig. 2. CdSe, hex. Exciton diffusion coefficients parallel and perpendicular to the c axis vs temperature. Solid curves are to guide the eye. The inset shows the ratio D /D [93E].
Fig. 3. CdSe, hex. Diffusion length L x of excitons vs temperature. The solid curve is to guide the eye [93E].
Fig. 4. CdSe, hex. Temperature dependence of the self-diffusion coefficient of Cd ions [91F].