Electroreflectance Spectra of InGaN/AlGaN/GaN p-n-Heterostructures

ABSTRACTElectroreflectance (ER) spectra of InGaN/AlGaN/GaN p-n- heterostructures with multiple quantum wells (MQW) are studied. Structures with MQW InGaN/GaN were grown for blue LEDs by MOCVD technology and “flip-chip” mounted. The ER spectral maxima correspond to the high energy side of electroluminescence spectral line. The ER spectra caused by Franz-Keldysh effect are approximated by Aspnes theory. The ER spectra in a range 400 ÷ 800 nm have interference bands caused by the change of refraction index in the structure.

Emission Characteristics of GaN-Based EL Device with AC Operation

ABSTRACTGaN-based electroluminescence devices (ELDs) were fabricated using a GaN powder as an emission layer. The electroluminescence spectra of the GaN ELDs under AC operation were observed at room temperature. The emission characteristics of GaN-based ELDs were studied to compare the EL spectra and the cathodoluminescence (CL) spectra. It was clarified that the EL spectra were similar to the CL spectra of a GaN emission layer. The emission peaks in the EL spectra were shifted toward the high-energy side with increasing operation frequency.

Effect of alkylation of ammonia on the optical band shape of solvated electrons

At 200 K the width at half height, W1/2, of the e−solv optical absorption band in n-propyl amine is 2.1-fold greater than that in ammonia. Three quarters of the broadening occurs on the high energy side of the band. The energy Er at half height on the low energy side of the band is nearly the same in the amine as in ammonia, while Eb, the energy at half height on the high energy side, is 42% greater in the amine. The temperature coefficient dEAmax/dT is 1.8-fold greater in the amine than in ammonia. The larger width is consistent with there being a less uniform distribution of localization sites in the system, and the larger temperature coefficient implies that the sites are more easily disturbed by thermal agitation. A quantum statistical mechanical model, such as the one begun by Simons, is needed to extend the theoretical treatment of e−solv spectra. The correlation between optical absorption energies of e−solv and the structure of the solvent, as partially reflected in the Kirkwood correlation factor, is re-emphasized.

X-Ray LIII Absorption Edges of Bismuth Halides

The position of the bismuth LIII absorption discontinuity has been studied in pure bismuth metal and in its halides, BiF3, BiCl3, BiBr3 and BiI3 using a focussing spectrograph of the transmission (Cauchois) type. In all these compounds the discontinuity is found to shift towards the high energy side with respect to that in the pure metal. The experimental material presented in this study convincingly shows that the position of the LIII absorption edge is determined by the partial charge of the absorbing atom and not by its valence.

Luminescence in KI:Tl

Freshly cleaved single crystals of KI:TI containing various concentrations of Tl have been irradiated in a vacuum monochromator in the 2800-1100 A region at temper. atures between -140 and 45 �0. The relative luminescence efficiencies in the Tl absorption bands and the host crystal fundamental absorption show that energy is transferred from host crystal to impurity centre to produce luminescence at room temperatures. To the high energy side of a threshold, which appears to depend on activator concentration, the luminescence efficiency is superlinear above about 15 �0 for KI:Tl (0�0005%).