Magnetoluminescence and Resonant Electronic Raman Scattering Investigation of Donors and Excitons in Hydride Vpe and Mocvd GaN

Abstract

The donor and exciton states in ultra high-quality heteroepitaxial GaN grown by hydride vapor phase epitaxy (HVPE) and metalorganic chemical vapor deposition (MOCVD) on sapphire substrates are investigated using low temperature photoluminescence (PL), reflectance, magnetospectroscopy in fields up to 12 T, and resonant electronic Raman scattering (RERS). The A free exciton is confirmed to have a binding energy of about 26.4 meV, independent of strain in the material. Bound n=2 exciton peaks are distinguished in the PL spectrum by their thermalization and sample dependence. The Si donor is shown to have a binding energy of about 21 meV using Si-doped HVPE samples grown at Epitronics. Up to five additional residual donor species are observed when comparing various HVPE and MOCVD samples. Pronounced temperaturedependence of the two-electron satellites is observed, suggesting the existence of unresolved excited rotator states of the neutral donor-bound exciton. Highly resolved magnetic splitting patterns are observed in the two-electron satellites. A nonperturbative theory of these donor splittings is developed, including anisotropy. Resonant electronic Raman scattering from residual donors is reported, and yields improved linewidths compared to PL.

Photoluminescence, Magnetospectroscopy, and Resonant Electronic Raman Studies of Heteroepitaxial Gallium Nitride

“…The two peaks just below the PL peak are assigned to n=2 A excitons bound to impurities, based on the variation in their strength relative to from sample to sample and on their tendency to quench relative to the peak as the temperature is raised, as shown in Figure 3 above. These behaviors, along with our theoretical calculations of anisotropy splitting, tend to rule out any explanation of this splitting in terms of anisotropy or exchange splittings [12] [13]. Confirmation of the independence of exciton binding energy on strain has also been provided recently by Yamaguchi et al [35] The reflectance spectrum of Figure 7 was recorded in the conventional geometry, with the incident and reflected light traveling nearly parallel to the c-axis (σ polarization) and reflecting from the front surface of the epilayer.…”

“…The corresponding no-phonon peak is unresolved on the low energy side of the broadened principal (D o ,X) peak, but is visible in the phonon replicas because of the characteristically larger phonon coupling of (A o ,X) transitions. Further discussion of the Si-related levels has been given elsewhere [12] [14].…”

Near-Band Gap Selective Photoluminescence in Wurtzite GaN

“…This energy difference accurately corresponds to the two electron transitions (not shown here) systematically detected in our ELOG layers. As it was previously observed by Skromme et al [9], this main repliqua of I 2 at 1.8 K is rapidly quenched when the temperature is raised and disappears above 10 K. It should be noted that the ERS experiment reveals only one shallow donor centre with a binding energy estimated to 30.5 meV using a simple hydrogenic model. Fig.…”

MOCVD-Epitaxy on Free-Standing HVPE-GaN Substrates

“…The near bandgap photoluminescence of the overgrown HVPE demonstrates the advantage of homoepitaxy on a high-quality substrate, showing bound and free exciton peaks with narrow linewidths, similar to the quality of the HVPE substrate [13]. This contrasts with our overgrown MOCVD-GaN, where just a (donor or acceptor related ) bound exciton (BE) peak was observed (Fig.…”