Münster 1997 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 40: Poster III

HL 40.90: Poster

Freitag, 21. März 1997, 11:00–14:00, Z

Metastable Photoconductivity in n-type GaN — •Michèle T. Hirsch, J. A. Wolk, W. Walukiewicz, and E. E. Haller — Lawrence Berkeley National Laboratory and University of California at Berkeley 1 Cyclotron Rd., 94720, CA, Berkeley, USA

We have observed persistent photoconductivity (PPC) in MOCVD grown unintentionally doped n-type GaN films (N_d≈ 10¹⁷cm⁻³). We measure the small signal conductance of the GaN between two coplanar ohmic contacts. At 77K, the conductivity of the sample changes by as much as a factor of two when exposed to light. After the excitation is removed the conductivity is still 80% greater than before exposure, even after 10⁴s. Similar effects are observed at room temperature but the changes are smaller. We have measured the temperature dependence of the light induced conductivity, and use these data to model the observed behavior. Using a Cary 2390 spectrometer as a source of monochromatic light, we have also observed the spectral dependence of the cross section for the absorption which gives rise to these conductivity changes. PPC has recently been reported for Mg doped p-type GaN and has been attributed to a metastability of the impurities in that material [1]. To our knowledge this is the first time PPC has been observed for n-type GaN. We will discuss possible explanations for these effects, including metastable defects and strain.

[1] C. Johnson et al. , Appl. Phys. Lett. 68, 1808, (1996). Work supported by US DOE under contract DE-AC03-76SF00098.