Nanocrystal Si (nc-Si) sensitization of Er in a silica matrix to obtain high optical activity in a Si-compatible material is investigated. Er-doped silicon-rich silicon oxide (SRSO) films, which consist of nc-Si embedded inside an SiO2 matrix, were deposited by electron-cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) using SiH4 and O2 with concurrent sputtering of Er followed by a high temperature anneal. For comparison, Er-free SRSO films were also deposited. Detailed investigation of processing conditions indicates that an annealing process consisting of 30 min anneal at 950°C without hydrogenation to be optimum for activation of Er. Investigation of MOS diode structure with Er-doped and Er-free SRSO films indicates that a mesa-type structure with n+ poly-silicon top contact, p-type substrate, and SRSO Si content of less than 40% gives the best diode performance. Er-free SRSO diodes fabricated using the optimum conditions show electroluminescence under forward bias. Er-doped SRSO diodes show photoresponse at 1.54 μm due to nanocrystal -- Er interactions, showing the promise of developing integrated, Si-based 1.54 μm light detectors for integrated microphotonic devices.
The role of the size of amorphous silicon quantum dots in the Er luminescence at 1.54 µm was investigated. As the dot size was increased, the more Er ions were located near one dot due to its large surface area and more Er ions interacted with other Er ions. This Er-Er interaction caused a weak photoluminescence intensity despite the increase in the effective excitation cross section. The critical dot size, needed to take advantage of the positive effect on Er luminescence, is considered to be about 2.0 nm, below which a small dot is very effective in the efficient luminescence of Er. However, the hydrogenation is considered to suppress this Er-Er interaction.