Opal consists of a three dimensional array of silica balls with diameter in the range 150 -350 nm and acts as a 3-D grating. Within the microcrystals (a few hundred microns) of opal there is typically 5% variation in ball diameter arranged in a fee structure. Using a specially modified MOCVD process InP can be grown within the voids between the touching silica balls. These interconnecting voids are approximately 1/5 and 2/5 the silica sphere diameter, Raman spectroscopy confirms the crystallinity of the InP for two samples loaded with 2.5 volume % of InP. The LO phonon is shifted to the red by 10 cm−l from the bulk value of 345 cm−1, while the TO phonon is shifted 22 cm−l to the blue from the bulk value of 303.7 cm−l. This shift is attributed to strain in the nanocry stals.
The half width of the reflectance is dependent upon InP loading with the 2.5 vol.% samples giving 0.19 eV and the lower loaded 0.4 vol. % giving 0.17 eV for samples with the same ball diameter. Photoluminescence emission near 1.7 eV is attributed to confined InP compared with a bulk value of 1.4 eV. The energy of the emission is determined by the combined contribution of the laterally confined InP and its interaction with the opal matrix.