(Invited) Impact of Boron Doping and H2 Annealing on Light Emission from Ge/Si Core-Shell Quantum Dots

Abstract

Light emission from Si/Ge based nanostructures has attracted much attention in the field of Si-based photonics because of its potential to combine photonic processing and electronic processing in a single chip. In our previous works[1, 2], we have demonstrated high-density formation of Ge-core/Si-clad quantum dots (QDs) by controlling the alternate thermal decomposition of GeH4 and SiH4 on thermally-grown SiO2 and shown that, in a single layer of QDs having a ~6.0 nm Ge-core and a ~3.0 nm-thick Si-clad in average size, stable photoluminescence (PL) obtained under 976nm photoexcitation in the energy region from 0.66 to 0.88 eV consists of four Gaussian components originating from radiative recombination through quantized states in the QDs as verified from dot size dependence of the PL peak energy and temperature dependence of PL properties. Possible ways to enhance the radiative recombination rate in photoexcited QDs are considered to reduce non-radiative centers and to increase carrier density with impurity doping into the QDs.In this work, we fabricated Si-QDs with B-doped Ge core and characterized their PL properties. In addition, we also evaluated the impact of H2 post-annealing on the PL properties. The Si-QDs with B-doped Ge core of ~4.6 nm in an average core height were formed on ~2.0 nm-thick SiO2 layer, where B-doping was carried out by pulse injection of 1% B2H6 diluted with H2 during the Ge deposition. First, we have confirmed that, stable room temperature PL observed in the energy range from 0.62 to 0.85 eV is increased by a factor of 2.4 with B-doping into the Ge cores. Notice that for the Si-QDs with the B-doped Ge core, a new PL component peaked at ~0.64 eV emerges in addition to the above-mentioned four components seen in non-doped QDs and is attributable to radiative recombination between the first quantized state in the conduction band and the B-acceptor level in the Ge cores. We have also found that the PL intensity becomes more than double when the sample was annealed at 350°C under an atmosphere of pure H2 with almost no change in the spectral shape while the PL intensity remains unchanged with anneal under an atmosphere of pure N2. Considering the fact that the PL intensity is decreased markedly with higher temperature anneal, this result is interpreted in terms of hydrogen passivation of residual defects in the Ge core and at the Si-clad/Ge-core interface.