Optical Properties of Nano Crystalline InP in Opal 3-Dimensional Gratings
- PDF / 328,401 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 14 Downloads / 151 Views
Opal is a natural grating for visible light consisting of regularly spaced balls of silica. These refracting properties give precious opal value as a gem stone. The refracting properties of opal alone (bare opal) are insufficient to produce a complete stop band in all directions for light transmission. Material with a complete stop band or Photonic Band Gap (PBG) is potentially useful for zero threshold current lasers and other optoelectronic devices. Very high efficiency is possible because a complete PBG will not allow any mode to propagate; however, an irregularity subsequently introduced within the PBG will allow only one mode of emission to propagate. Full PBGs have been demonstrated in the microwave region [1] using wire meshes and in colloidal liquids with polystyrene balls [2]. A solid system such as opal would have obvious processing advantages and could operate in the visible region. The silica balls comprising opal are arranged in the fcc configuration. Theoretical calculations [3] show that this arrangement and the small refractive index contrast between silica and air do not allow a complete photonic gap. However, between the touching silica balls an interconnecting array of voids may be filled with a suitable material. InP has a high refractive index, and as a semiconductor is an optical gain medium. Here we report on the optical properties of indium phosphide grown within the 3-dimensional opal gratings.
269 Mat. Res. Soc. Symp. Proc. Vol. 452 01997 Materials Research Society
EXPERIMENTAL DETAILS Samples and growth method Samples of synthesised opal were impregnated with InP using a specially modified MOCVD process [4]. Firstly, trimethylindium was added in a flow of hydrogen at 520 C in a standard MOCVD atmospheric pressure reactor. Secondly phosphine was passed through the reactor for several hours at 3500 C to decompose the hydride. For higher loadings of InP the above cycle was repeated. The opal had ball diameters in the range of 189 to 304 nm, measured by SEM with microcrystallites -100 lim in size and were in the form of polished plates, 0.5 mm thick and area of 25 mm 2 . Two samples were loaded to 2.5 volume % and the remainder low loaded samples contained 0.4 volume % of InP measured as by electron-microprobe analysis. Experimental techniques Raman spectra were measured in near backscattering configuration using 514.5 nm excitation from an Ar+ laser and charge coupled device detector. Photoluminescence spectra were measured by 457.9 nm excitation from an Ar+ laser and collected by a double monochromator and photomultiplier tube. All spectra were corrected for spectral response. Reflectance spectra were taken using a single spectrometer and integrating sphere. RESULTS
AND DISCUSSION
Raman spta We first examined the Raman spectra opal-InP. Raman spectra could only be obtained for the highly loaded samples. One sample (blue in colour) contained a range of ball sizes from 189 to 232 nm and is shown as the solid trace in fig. 1. The dashed line shows a sample (dark green in colour) with unif
Data Loading...
