ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
The photoluminescence (PL) at λ≤850 nm of boron-doped porous Si films anodically etched, passively etched, annealed, and reactive ion etched (RIE) under systematically varied conditions is described and discussed. As previously observed, the PL yield η of films etched from 7 to 20 Ω cm wafers in HF/H2O/C2H5OH solutions rapidly degraded during 40 mW illumination in air at 488 nm. In addition, it was totally quenched by O2 annealing or RIE but not by H2 RIE. However, the yield of films etched in HF/H2O only decreased by less than 10% following similar illumination for 7 h, and O2 annealing or RIE reduced it by 0%–50% only. The instability under illumination, the effects of oxygen annealing and RIE, Auger line shape measurements, and surface charge buildup during Auger analysis are consistent with a significantly higher density of weak Si—Si bonds in films etched in ethanol-containing solutions. These bonds are apparently broken by photoinduced oxidation, oxygen annealing, or O2 RIE, but the oxygen does not efficiently passivate the newly generated dangling bonds. While the peak emission wavelength λmax of the films etched from these wafers shifted with annealing and etching conditions, it invariably peaked in the ∼7600–8600 A(ring) range; η reached ∼1.7%. H2 RIE had no effect on η, but λmax was blueshifted. This behavior is attributed to similar breaking of weak Si—Si bonds followed by efficient passivation of the newly generated dangling bonds.The blueshift results from the higher H/Si ratio; the invariant yield is believed to be limited by the density of dangling bonds at the SiOxHy/Si interface which is apparently unaffected by the treatments. It is therefore believed that the PL is at least partially due to SiHx or SiOxHy complexes on the crystallite and column surfaces, which are similar to those found at the surface of some H-rich a-Si:H. Size effects, however, cannot be ruled out. In contrast to films etched from 7 to 20 Ω cm wafers, λmax of those prepared from 1 to 2 Ω cm substrates was consistently ∼7000 A(ring) after a brief exposure to air. While η exhibited a complex dependence on the O2 RIE power, λmax was unchanged by either O2 or H2 plasmas. The emission from heavily doped ∼0.02 Ω cm films was usually undetectable. However, H2 RIE resulted in observable PL. © 1995 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.358630
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