Zn-doped InP layers were obtained by two different doping techniques: in situ doping by low pressure metalorganic chemical vapor deposition, and thermal diffusion from a Zn-containing film. Their low temperature photoluminescence ͑PL͒ characteristics were studied, and compared. In Zn-diffused InP, the deep donor to acceptor transition was the most dominant transition and other transitions such as the band edge transition and the band to band or shallow donor to acceptor transition were not observed at the excitation power of 10 mW. On the other hand, well resolved band edge peaks and the band or shallow donor to acceptor transition peak were observed for in situ Zn doped InP, implying that less interstitial Zn atoms were generated during in situ doping. Saturation of the hole concentration at 1.5ϫ1018 cm 3 was observed in in situ Zn doped InP, and the changes in PL characteristics at the saturation level were extensively studied. Two new deep bands at 0.88-1.0 eV and 1.21-1.27 eV were observed, and the intensity of the lower energy band increased with diethylzinc flow rate. The lower energy band was observed even at room temperature, and it is presumed to be related with the saturation of hole concentration.

No abstract

No abstract

Laser excitation studies of CaF2 crystals doped with 0.01 to 10% Ho3+ using the second harmonic wavelength 532 nm of a pulsed Nd: YAG laser are carried out. Three fluorescence bands belonging to the 5F4, 5S2 → 5I8, 5F4, 5S2 → 5I7 and 5F5 → 5I8 transitions are detected. Fluorescence lifetimes of the first two transitions are measured and used for site‐identification of new lines. Four upconverted fluorescence bands belonging to the 5F3 → 5I8, 5G4 → 5I8, 5G5 → 5I8, 5H5, 5H6 → 5I8 transitions are also detected. A comparative study is made of two pairs of energy transfer mechanisms, which are multiphonon relaxation versus ion‐pair relaxation and two‐photon absorption versus ion‐pair relaxation. The analysis of the concentration dependence of fluorescence intensities shows that ion‐pair relaxation is the chief mechanism responsible for the fluorescence and upconversion behaviour of CaF2:Ho3+.

In this paper, we have investigated the bandgap tuning in the InGaAs (P)/ InP multiquantum well (MQW) structure obtained by impurity-free vacancy diffusion (IFVD) using low temperature photoluminescence (PL). The MQW intermixing was performed in a rapid thermal annealer (RTA) using the dielectric capping materials, Si02 and SiNX. The Si02 capping was successfully used with InGaAs cap layer to cause a large bandgap tuning effect in the InGaAs/InP MQW material. The blue shift of bandgap energy after RTA treatment was as much as 185 and 230 meV at 750 t and 850 t, respectively, with its value controllable using annealing time and temperature. Samples with Si02-InP or SiN-InGaAs cap layer combinations, on the other hand, did not show any significant energy shifts. The absorption spectra taken from the same samples confimed the energy shifts obtained using PL. The process developed can be readily applied to fabrication of photodetectors that are sensitive to wavelength and/or polarization.