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Effects of threading dislocations and other defects on reduction of band-edge photoluminescence in n-InN films
|Yoshihiro Ishitani , Kenta Kato , Hitoshi Ogiwara , Akihiko Yoshikawa
Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
Recent progress of InN growth led to the decrease in residual electron density ne0 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 ne0 ((2 – 10)´1017 cm-3) in the bulk region except for the surface or interface accumulation region. The edge and screw type dislocation densities (ned and nsc) were obtained from the peak widths in XRC of (0002) and (10-10) diffractions, respectively. The temperature dependence of PL intensity, IPL, was obtained by spectral integration in a region of 0.54 – 0.85 eV.
IPL was normalized as IPL/ne0, since IPL is proportional to ne0 under weak carrier excitation density of 1014 – 1015 cm-3. We have found that IPL/ne0 at 16 K decreases with ned and ne0. A sample with large ned of 2.5´1010 cm-2 had small IPL/ne0 at 16 K in spite of small ne0 (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 IPL/ne0 decreased with temperature without correlation with ned or nsc; the parameters obtained from the successful fitting of a model function of IPL with thermal activation to the experimental data had no correlation with ned, nsc, or ne0. 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.
Presentation: Oral at E-MRS Fall Meeting 2009, Symposium A, by Yoshihiro Ishitani
See On-line Journal of E-MRS Fall Meeting 2009
Submitted: 2009-05-10 13:48 Revised: 2009-06-07 00:48