Red-green luminescence in indium gallium nitride alloys investigated by high pressure optical spectroscopy

Raman and photoluminescence mapping of InxGa1−xN (x ∼ 0.4) at high pressure: Optical determination of composition and stress

“…The pressure slope, obtained including datasets from all three sites, is 30(2) meVÁGPa À1 . This value is in accordance with experimental high pressure absorption studies of In x Ga 1Àx N films 6,25 and theoretical works for compositions relevant to our sample and assuming uniform arrangement of the In atoms. 5,27 With respect to the existing literature on high pressure PL measurements for x $ 0.4, our value is somewhat higher than that obtained by Franssen et al ($26 meVÁGPa À1 ) 5 and significantly larger than that more recently reported by Millot et al ($19 meVÁGPa À1 ), where the reduced pressure slope of the PL peak compared and absorption spectrum of the asgrown In x Ga 1Àx N sample at ambient conditions.…”

“…Despite the extensive studies reported in the literature so far, the origin of the PL in these materials is still under debate, alternating between bandto-band transitions (and therefore closely lying and identifying the absorption edge) 5 to defect states within the energy bandgap (and thus more or less irrelevant to the bandgap). 6 The results in this study clearly support the former case. Raman spectroscopy is also a well-established, non-destructive optical technique for assessing the crystalline structure, quality, stress distribution, and free carrier concentration of nitride semiconducting systems.…”

“…6 The radiative recombination associated with highly localized states as the origin of the PL peak was also the reasoning for its $4 times smaller pressure slope in the early work of Li et al 25 The importance of the laser power used for PL excitation-in combination with the laser wavelength and the corresponding absorption coefficient-should not be overlooked as excessive values could also affect the ambient and the high pressure PL spectra and hence the pressure slope. In any case, our results suggest that as long as the sample is of sufficient quality, the PL peak refers to the band-to-band transitions and it can be used to probe the pressure evolution of the fundamental energy gap, contrary to the conclusions of Millot et al 6 As in the In x Ga 1Àx N system the Raman peak frequencies and the PL peak energy (E PL ) are affected by both the In content and the residual stress, the optical spectroscopic data can be in principle exploited for the estimation of the two parameters in an unknown sample. In Figure 3, the correlation plot of the E PL vs. E 2 2 mode frequency (x E2 ) for the as-grown (solid star) and the powdered sample (open star) as well as for the high pressure data (circles) is illustrated.…”

High-pressure optical absorption in InN: Electron density dependence in the wurtzite phase and reevaluation of the indirect band gap of rocksalt InN

“…[6][7][8][9][10] In general, the pressure dependence of the optical-emission peak energy in InN and InGaN is weaker than that of the absorption edge. 6,10 The observed differences have been attributed to a sizable contribution of impurity states to the optical emission of the samples. Other authors, however, by direct comparison of PL data with pressure coefficients obtained with ab initio calculations, conclude that the PL emission from w-InN and InGaN has a mainly band-to-band character.…”

“…In turn, several works have studied the pressure dependence of the fundamental band gap of w-InN and InGaN. [6][7][8][9][10] In general, the pressure dependence of the optical-emission peak energy in InN and InGaN is weaker than that of the absorption edge. 6,10 The observed differences have been attributed to a sizable contribution of impurity states to the optical emission of the samples.…”