Low Stokes shift in thick and homogeneous InGaN epilayers

Abstract

The optical properties of thick InxGa1−xN layers have been studied using optical absorption and cathodoluminescence techniques. The indium composition x of the layers ranged from 0.03 to 0.17 as determined by Rutherford backscattering measurements. The difference between the band gap and the peak emission energy (Stokes shift) was found to be considerably smaller than reported in the past for these alloys. Monochromatic images show that light emission from most of the film is homogeneous and is associated with a low Stokes shift. A second emission band at longer wavelengths is observed for x⩾0.08. This band originates from indium-rich regions in the vicinity of extended defects, and exhibits a larger Stokes shift. Our observations indicate that it is possible to grow InGaN epilayers with high indium composition, high homogeneity, and lower Stokes shift.

Imaging of InGaN inhomogeneities using visible apertureless near-field scanning optical microscope

“…The broadened X-ray diffraction peak seen in the insert in Dependences of the absorption edge and luminescence energy on the mole fraction of In in an InGaN alloy have been previously reported. 30,31 The indium content, which corresponds to the 420 nm PL peak position is ~10-15%, and this agrees very well with the indium fraction obtained from X-ray diffraction (~14%). The stronger peak at 480-520 nm corresponds to the indium content of ~15-20%, which is also possible in our sample.…”

Response to “Comment on ‘Direct evidence of nanocluster-induced luminescence in InGaN epifilms’ ” [Appl. Phys. Lett. 87, 136101 (2005)]

“…8 Our XRD measurements clearly indicate strong indium aggregation processes in our sample and this observation is in agreement with previous reports. [4][5][6][7][8] The comments also argued the interpretation of our scanning electron microscopy ͑SEM͒ and energy dispersive x-ray spectrometry ͑EDS͒ results. Our InGaN films have been found to have mirrorlike surface by scanning electron microscopy ͑SEM͒ and transmission electron microscopy ͑TEM͒ measurements.…”

“…However, by selectively focusing the electron beam inside and outside the cluster, we have demonstrated that the double CL peak arises from phase segregation. Srinivasan et al 8 have also performed CL images and clearly shown that composition fluctuations do contribute to the CL spectra. It is not a consequence of partially relaxed InGaN films of uniform indium composition.…”

“…Besides, there are many other excellent works that reported the observation of nanoscale indium composition fluctuations due to phase separation by different techniques. [6][7][8][9][10][11][12][13] For example, it was found that in the growth of InGaN films, the composition pulling effect is inevitable and plays an important role in the microstructure. It initially inhibits the incorporation of In during the earlier stages.…”

Raman scattering by the E2h and A1(LO) phonons of InxGa1−xN epilayers (0.25 < x < 0.75) grown by molecular beam epitaxy

“…Such CL signal, arising from regions with slightly larger In contents, is fully compatible with the broadening of the HRXRD reflections and may be attributed to dot-like In-rich regions near the surface of the InGaN epilayers. 31,32 In the rest of epilayers the CL signal was highly homogeneous, with no evidence of InN-rich segregated phases. B. Raman scattering by A 1 (LO) and E 2h phonons Figure 3 shows Raman spectra of four representative In x Ga 1Àx N epilayers.…”