Examination of (crystallized a-Ge:H)/a-SiNx:H multilayers which display photoluminescence

A study has been conducted of (crystallized a-Ge :H)/a-SiN x :H multilayers which display room temperature photoluminescence in the visible range. The a-Ge :H/a-SiN x :H multilayers were prepared by glow discharge chemical vapor deposition by changing gas flows in a continuous deposition using a computer. Crystallization of the a-Ge :H layers was achieved by either thermal annealing in vacuum or exposure to a scanning laser light. The multilayer structure was confirmed by glancing angle X-ray diffraction. Crystallization was confirmed by Raman scattering. When crystallization of the a-Ge :H is achieved using the laser-scanning technique, strong visible photoluminescence with a peak centered around 625 nm, independent of the a-Ge :H layer thickness, is observed. The crystallization is accompanied by severe cracking and pitting of the film. A study of several a-Ge :H/a-SiN x :H layered structures reveals that this laser-induced crystallization only occurs when the a-Ge :H is in a state of high stress. Further study reveals that a-SiN x :H also photoluminesces with a similarly broad peak in the same wavelength range as observed from the crystallized multilayers. Using slow thermal annealing, it was possible to crystallize the a-Ge :H with minimal physical damage to the film. Photoluminescence measurements of these quantum-well structures yield a low intensity broad peak in the visible range before crystallization which does not change after crystallization. One is led to conclude that the photoluminescence observed in the laser-crystallized a-Ge :H/a-SiN x :H is from the a-SiN x :H and cannot be attributed to effects of quantum confinement.