Photoluminescence from n-(p-) type impurity doped Si nanocrystals
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Photoluminescence from n- (p-) type impurity doped Si nanocrystals Minoru Fujii1, Atsushi Mimura1, Shinji Hayashi1, Dmitri Kovalev2 and Frederick Koch2 1 Department of Electrical and Electronics Engineering, Faculty of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan 2 Technische Universität München, Physik-Department E16, D-85747 Garching, Germany
ABSTRACT
Effects of impurity (P and B) doping on the photoluminescence (PL) properties of Si nanocrystals (nc-Si) in SiO2 thin films are studied. It is shown that with increasing P concentration, PL intensity first increases and then decreases. In the P concentration range where PL intensity increases, quenching of the defect-related PL is observed, suggesting that dangling-bond defects are passivated by P doping. On the other hand, in the range where PL intensity decreases, optical absorption due to the intravalley transitions of free electrons generated by P doping appears. The generation of free electrons and the resultant three-body Auger recombination of electron-hole pairs is considered to be responsible for the observed PL quenching. In the case of B doping, the behavior is much different. With increasing B concentration, PL intensity decreases monotonously. By combining the results obtained for P and B doped samples, the effects of donor and acceptor impurities on the PL properties of nc-Si are discussed. INTRODUCTION Since the discovery of visible photoluminescence (PL) from porous-Si, optical properties of Si nanocrystals (nc-Si) have intensively been studied. Application of nc-Si to commercial devices requires deeper knowledge of their energy band structure. In particular, the information related to the electronic properties of impurity atoms is essential, since for nanometer-sized crystallites a high impurity concentration can be realized by doping a single nanocrystal with only one impurity atom. Thus the electrical and optical properties of nc-Si are expected to be very sensitive to doping level. However, it has not been fully understood how a dopant atom works in such a confined and dielectric discontinuous medium. In this work, the effects of P and B doping on the PL properties of nc-Si are studied. By combining the results obtained for P and B doped samples, the behavior of donor and acceptor impurities in nc-Si is discussed. SAMPLE PREPARATION Si nanocrystals in oxide matrices were prepared by an rf cosputtering method. Pure nc-Si were prepared by the cosputtering of Si and SiO2 (99.99%) and the post-annealing at temperatures higher than 1100°C [1]. Phosphorous (Boron) doped nc-Si were prepared by cosputtering Si and phosphosilicate (PSG) [bolosilicate (BSG)] glasses [2-6]. P- (B-) doped nc-Si are thus embedded in PSG (BSG) matrices. P (B) concentration was controlled by changing the ratio of P2O5 (B2O3) with respect to SiO2 in PSG (BSG) sputtering targets. The highest concentration of P2O5 (B2O3) in sputtering F9.2.1
Intensity (Normalized)
1.4 1.2
nc-Si in SiO 2 9.0 nm
295 K
diam eter
1.0
2.5 nm
0.8 0.6 0.4
Figure 1.
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