Recent progress of InN growth led to the decrease in residual electron density n_e0 to 10¹⁷ cm^-3. As a material of light emitting devices, radiative efficiency and non-radiative recombination processes are the most important issues to be uncovered. There are a lot of defects such as edge-type threading vacancies and dislocations producing residual electrons. Although carrier recombination processes were studied by several groups, defects inducing non-radiative recombination or recombination via deep levels have not been uncovered yet. In this report we show two those non–band edge recombination (NBER) processes for InN samples of the state of the art.

The samples grown by RF-MBE had In-polarity and n-type conductivity. We have reported the importance of edge type dislocations and point defects in carrier scattering in these samples by IR-reflectance analysis, which also revealed n_e0 ((2 – 10)´10¹⁷ cm^-3) in the bulk region except for the surface or interface accumulation region. The edge and screw type dislocation densities (n_ed and n_sc) were obtained from the peak widths in XRC of (0002) and (10-10) diffractions, respectively. The temperature dependence of PL intensity, I_PL, was obtained by spectral integration in a region of 0.54 – 0.85 eV.

I_PL was normalized as I_PL/n_e0, since I_PL is proportional to n_e0 under weak carrier excitation density of 10¹⁴ – 10¹⁵ cm^-3. We have found that I_PL/n_e0 at 16 K decreases with n_ed and n_e0. A sample with large n_ed of 2.5´10¹⁰ cm^-2 had small I_PL/n_e0 at 16 K in spite of small n_e0 (2.5´10¹⁷ cm^-3), indicating the existence of an NBER process taking place around edge-type dislocations without threshold energy. On the other hand I_PL/n_e0 decreased with temperature without correlation with n_ed or n_sc; the parameters obtained from the successful fitting of a model function of I_PL with thermal activation to the experimental data had no correlation with n_ed, n_sc, or n_e0. There is another process with threshold energy and originating from defects such as vacancies or impurities except for dislocations. PLE spectra also supported the two recombination processes without and with threshold energy (< 100meV). From consideration on configuration coordinate in NBER, we conclude the importance of the defects except for the dislocations and processes without threshold energy around edge-type dislocations.

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