Skip to main content Accessibility help
×
Home

Influence of Deposition Conditions on the optical and Electronic Properties of a-Ge:H

  • W. Paul (a1), S. J. Jones (a1), F. C. Marques (a1), D. Pang (a1), W. A. Turner (a1), A. E. Wetsel (a1), P. Wickboldt (a1) and J. H. Chen (a2)...

Abstract

We have measured the optical absorption edge spectra for absorption coefficients between 1 and 105 cm-1, the photoluminescence spectra at 77 K, the conductivity-temperature relations, and the photoconductivity magnitude and spectral dependence for a series of r.f. glow discharge films of a-Ge:H. The films were deposited at the powered cathode and unpowered anode of a diode capacitive reactor having very different electric fields and plasma conditions, while substrate temperature, H2 dilution of a GeH4 plasma and applied r.f. power were varied. The structure of the films are radically different, with the anode-deposited films displaying a microstructure of low density material (voids) and the cathode-deposited films displaying homogeneity similar to that of device-quality a-Si:H. A self consistent explanation of the differences in measured optical and electronic properties is given, taking full account of the structural observations. From this analysis the conditions required for the production of a-Ge:H of good photoelectronic quality may be inferred. Preliminary structural, optical and photoelectronic data for a-Si1.x Gex :H of large x, prepared under conditions extrapolated from the a-Ge study, indicate significant improvements from current data in the literature.

Copyright

References

Hide All
1 For early reviews, see Amorphous and Liquid Semiconductors, edited by Tauc, J. (Plenum, New York, 1974).
2 An extensive review of the properties of optimized unhydrogenated a-Ge:H is given in work by Paul, W., Connell, G.A.N. and Temkin, R.J., Adv. Phys. 22, 529(1973).
3 Chittick, R.C., Alexander, J.H. and Sterling, H.F., J. Electrochem. Soc. 116, 77 (1969).
4 Spear, W.E. and LeComber, P.G., J. Non-Cryst. Solids 8–10, 727 (1972).
5 LeComber, P.G. and Spear, W.E., Phys. Rev. Lett. 25, 509 (1970).
6 Spear, W.E. and LeComber, P.G., Solid State Commun. 17, 1193 (1975);
Carlson, D.E. and Wronski, C.R., Appl. Phys. Lett. 28, 671 (1976).
7 Lewis, AJ., Connell, G.A.N., Paul, W., Pawlik, J.R. and Temkin, R.J., A.I.P. Conf. Proc. 20, 27 (1974).
8 Triska, A., Dennison, D. and Fritzsche, H., Bull. Am. Phy. Soc. 20, 392 (1975).
9 Lewis, A.J., Phys. Rev. B14, 658 (1976);
Connell, G.A.N. and Pawlik, J.R., Phys. Rev. B13, 787 (1976).
10 Chevallier, J., Wieder, H., Onton, A. and Guarnieri, C.R., Solid State Commun. 26, 867 (1977);
Marfaing, Y., in Proc. 2nd E.C. PVSEC. edited by Reidel, D. (Kluwer, Dordrecht, 1979), p. 287.
11 Paul, W. in Fundamental Physics of Amorphous Semiconductors, edited by Yonezawa, F. (Springer Series in Solid State Sciences 25, Springer-Verlag, New York, 1980), p. 72;
Paul, D.K., von Roedem, B., Oguz, S., Blake, J. and Paul, W., J. Phys. Soc. Japan 49, 1261 (1980);
Hauschildt, D., Fisher, R. and Fuhs, W., Phys. Stat. Solidi (b) 102, 563 (1980);
Karg, F., Kruhler, W., Moller, M. and von Klitzing, K., J. Appl. Phys. 60, 2016 (1986);
Street, R.A., Tsai, C.C., Stutzmann, M. and Kakalios, J., Phil. Mag. B56, 289 (1987);
Aljishi, S., Chu, V., Smith, Z.E., Shen, D.S., Conde, J.P., Slobodin, D., Kolodzey, J. and Wagner, S., J. Non-Cryst. Solids 97/98, 1023 (1987);
Mackenzie, K.D., Burnett, J.H., Eggert, J.R., Li, Y.M. and Paul, W., Phys. Rev. B38, 6120 (1988);
Stutzmann, M., Street, R.A., Tsai, C.C., Boyce, J.B. and Ready, S.E., J. Appl. Phys. 66, 569 (1989);
Wagner, S., Chu, V., Conde, J.P. and Liu, J.Z., J. Non-Cryst. Solids 114, 453 (1989);
Fuhs, W. and Finger, F., J. Non-Cryst. Solids 114, 387 (1989), and references therein. For additional papers on a-si1 x Gex :H alloys, see Mat. Res. Soc. Symp. Proc. 192 (MRS, Pittsburgh, 1990).
12 See, for example, Matsuda, A. and Tanaka, K., J. Non-Cryst. Solids 97/98, 1367 (1987).
13 Paul, W. in Amorphous Silicon and Related Materials, edited by Fritzsche, H. (World Scientific, New Jersey, 1989), p. 63;
Fortman, C.M. in Amorphous Silicon Technology, edited by Madan, A., Thompson, M.J., Taylor, P.C., LeComber, P.G. and Hamakawa, Y. (Mat. Res. Soc. Proc. 118, Pittsburgh, 1988), p. 691.
14 Yan, P., Lichtin, N.N. and Morel, D.L., Appl. Phys. Lett. 50, 1367 (1987);
Slobodin, D., Aljishi, S. and Wagner, S. in Plasma Processing and Synthesis of Materials, edited by Apelian, D. and Szekely, J. (Mat. Res. Soc. Proc. 98, Pittsburgh, 1987), p. 291;
Marques, F.C. and Chambouleyron, I. in Proc. 9th E.C. PVSEC. edited by Palz, W., Wrixon, G.T. and Helm, P. (Kluwer, Dordrecht, 1989), p. 1042;
Martin, D., Schroder, B., Leidner, M. and Ochsner, H., J. Non-Cryst. Solids 114, 537 (1989);
Aoki, T., Kato, S., Nishikawa, Y. and Hirose, M., J. Non-Cryst Solids 114, 798 (1989);
Karg, F.H., Bohm, H. and Pierz, K., J. Non-Cryst. Solids 114, 477 (1989);
Turner, W.A., Jones, S.J., Pang, D., Bateman, B.F., Chen, J.H., Li, Y.M., Marques, F.C., Wetsel, A.E., Wickboldt, P., Paul, W., Bodart, J., Norberg, R.E., El Zawawi, I. and Theye, M.L., J. Appl. Phys. 67, 7430 (1990);
Godet, C., Chu, V., Equer, B., Bouizem, Y., Chahed, L., El Zawawi, I., Theye, M.L., Basour, S., Bruyere, J.C. and Stoquert, J.P. in Amorphous Silicon Technology-1990, edited by Taylor, P.C., Thompson, M.J., LeComber, P.G., Hamakawa, Y. and Madan, A. (Mat. Res. Soc. Proc. 192, Pittsburgh, 1990), p. 163;
Karg, F.H., Hirschauer, B., Kasper, W. and Pierz, K., to be published in Solar Energy Materials (1991).
15 Rudder, R.A., Cook, J.W. and Lucovsky, G., Appl. Phys. Lett. 43, 871 (1983);
Payson, J.S. and Ross, R.C., J. Non-Cryst. Solids 77/78, 579 (1985).
16 Turner, W.A., Jones, S.J., Pang, D., Bateman, B.F., Chen, J.H., Li, Y.M., Marques, F.C., Wetsel, A.E., Wickboldt, P., Paul, W., Bodart, J., Norberg, R.E., El Zawawi, I. and Theye, M.L., J. Appl. Phys. 67, 7430 (1990).
17 Our earlier review (reference 11) had, in fact, already set out in some detail the argument for a microstructural explanation for the deteriorated properties of a-Ge:H and a-Si1−x Gex:H alloys compared with a-Si:H.
18 Turner, W.A., Pang, D., Wetsel, A.E., Jones, S.J., Paul, W. and Chen, J.H. in Amorphous Silicon Technology-1990, edited by Taylor, P.C., Thompson, M.J., LeComber, P.G., Hamakawa, Y. and Madan, A. (Mat. Res. Soc. Proc. 192, Pittsburgh, 1990), p. 493;
Paul, W., Jones, S.J. and Turner, W.A., Phil. Mag. B63, 247 (1991);
Paul, W., Jones, S.J., Turner, W.A. and Wickboldt, P., submitted to J. Non-Cryst. Solids;
Jones, S.J., Turner, W.A., Pang, D. and Paul, W., presented at MRS Fall Meeting 1990, to be published.
19 Mackenzie, K.D., Eggert, J.R., Leopold, D.J., Li, Y.M., Lin, S. and Paul, W., Phys. Rev. B31, 2198 (1985).
20 For an account of our experiments with Reactor 2, where Ts, H2 dilution, gas pressure, gas flow, r.f. power and electrode spacing were varied, see Wickboldt, P., Jones, S.J., Marques, F.C., Pang, D., Turner, W.A., Wetsel, A.E., Paul, W. and Chen, J.H., submitted to Phil. Mag. B.
21 Connell, G.A.N., Temkin, R.J. and Paul, W., Adv. Phys. 22, 643 (1973).
22 Theye, M.L., Optics Commun. 2, 329 (1970); Mat. Res. Bull. 6, 103 (1971).
23 We presume to call it “intrinsic” since, as far as we know, the edge is at least as sharp as any heretofore published for either a-Ge:H or a-Si:H.
24 For the same film depositions, the E0's estimated from steady state photoconductivity measured by CPM ranged between 40 and 55 meV, with 15 of the 16 at 50 meV or smaller.
25 Guha, S., Payson, J.S., Agarwal, S.C. and Ovshinsky, S.R., J. Non-Cryst. Solids 97/98, 1455 (1987);
Haku, H., Sayama, S., Nakashima, Y., Takahama, T., Isomura, M., Tarui, H., Hishikawa, Y., Tsuda, S., Nakano, S., Ohnishi, M. and Kuwano, Y., J. Appl. Phys. 26, 1978 (1987);
Wagner, S., Chu, V., Conde, J.P. and Liu, J.Z., J. Non-Cryst. Solids 114, 453 (1989).
26 We do not attempt an estimation of defect density by integration of α(hv) as is often done, as we believe this procedure to be flawed. See Li, Y.M. and Paul, W., this volume.
27 For these anode films, the steady-state photoconductivity is too low to permit an accurate evaluation of Eo from CPM measurements.
28 Our PL system (and procedures) have been described in Anderson, D.A., Moddel, G., Collins, R.W. and Paul, W., Solid State Commun. 31, 677 (1979). Excitation is by the 1.96 eV radiation from a HeNe laser with an illumination intensity of 100 mW/cm2. Our inability to observe PL in the anode films may be due to the sensitivity of our system, since earlier we were unable to detect PL in samples of a-Ge:H prepared at Marburg and measured by Carius before being supplied to us. Our detectivity limit is about a factor of 10 below the intensities measured for the cathode films. We note that it is the difference between our anode and cathode films which is significant for our present purposes.
29 Carius, R. in Amorphous Silicon and Related Materials, edited by Fritzsche, H. (World Scientific, New Jersey, 1989), p. 939.
30 If we assume that a mobility gap of 1.13 eV is obtained from a plot of (agra;hv)1/2 vs hv, the relaxation below the gap would be approximately 0.33 eV.
31 TS between 100 and 300o C; H2/GeH4 ratios between 10:1 and 40:1; power density at the cathode of Reactor 1 between 0.06 and 0.3 W/cm2; power density at the cathode of Reactor 2 between 0.25 and 0.65 W/cm2.
32 Li, Y.M., Turner, W.A., Lee, C. and Paul, W. in Amorphous Silicon Technology-1989, edited by Madan, A., Thompson, M.J., Taylor, P.C., Hamakawa, Y. and LeComber, P.G., (Mat. Res. Soc. Proc. 149, Pittsburgh, 1989), p. 187.

Metrics

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed