Structural order effect in visible photoluminescence properties of nanocrystalline Si:H thin films

Abstract

We report room-temperature visible photoluminescence (PL) properties of highly ordered hydrogenated nanocrystalline Si(nc-Si:H) with good electrical performance. The PL profiles can be well reproduced by the model of Islam and Kumar [J. Appl. Phys. 93, 1753 (2003)], incorporating the effects of quantum confinement and localized surface states, as well as a log-normal crystallite size distribution. Raman, PL, and electrical results consistently reveal that improvement of structural order within nc-Si:H is beneficial to enhance the PL efficiency. Owing to adequate order, strong visible PL and high electron mobility can coexist in nc-Si:H, which may provide possibilities in Si-based optoelectronics.

Electronic states in hydrogenated nanocrystalline silicon thin films detected by photocurrent technique

“…The experimental photoluminescence signal due to the recombination process was indeed ignorable in the weak absorption region (with photon energy below 1.15 eV) in the nc-Si:H thin film, as reported in Ref. 15. Therefore, the temperature-dependent photocurrent in the weak absorption can be simplified as a pure thermal activated behavior…”

“…With the photon energy increasing, the photocurrent amplitude increases quickly due to the absorption and photo excited carrier density increasing, where the recombination process becomes a more and more important factor. The experimental photoluminescence from the recombination process had been observed to start with a photon energy of 1.2 eV and achieve to its maximum around $1.8 eV, 15 where the direct transition has also been demonstrated by the power number x ¼ 0.5 in the second threshold photocurrent. Moreover, the recombination time is dependent on the escape time in the strong absorption region, because the lower possibility of recombination will be in the photo carriers with the higher transport mobility.…”

Band offsets and transport mechanisms of hydrogenated nanocrystalline silicon/crystalline silicon heterojunction diode: Key properties for device applications

“…1͑d͒, together with two broad ͓͑220͒ and ͑311͔͒ structures. The calculated average grain size from XRD is 4.8 nm, and it obeys a log-normal distribution with size dispersion around 4%, 10 which is obtained from the fitting result of the PL spectrum ͓solid curve in Fig. 1͑c͔͒ by the Islam and Kumar model.…”

“…6,7 Over the past ten years, we have devoted great efforts to the growth and characterization of highly ordered nc-Si:H films with thickness on the order of several microns. 8,9 Interesting phenomena have been observed such as structural order effect in visible photoluminescence ͑PL͒, 10 high electron mobility, 11 and periodical negative differential conductivity. 12 Although the conduction mechanism of the nc-Si:H thin film has been theoretically investigated, 13 device-grade HJ formed by nc-Si:H and crystalline Si ͑c-Si͒ is rarely reported compared with its HJ counterparts such as a-Si:H/c-Si, 14 hydrogenated multicrystalline silicon/a-Si, 15 nc-Si/multicrystalline Si, 16 etc.…”

Conduction behaviour of hydrogenated nanocrystalline silicon backward diode

“…Recently, besides artificial nanostructures, resonant tunnelling has also been observed in the Si nanocrystals which were naturally embedded in amorphous matrices as a so-called natural quantum confinement (NQC) system [4], which provided a new way to produce low dimension semiconductor material with advantages such as simple processing as well as low cost and so on. As an instance of NQC, a hydrogenated nanocrystalline silicon (nc-Si:H) film that is comprised of Si nanocrystals embedded in hydrogenated amorphous silicon (a-Si:H) matrices has attracted a great deal of attention due to its potential in microelectronic devices and photovoltaic applications as well as interesting physical properties that result from its heterogeneous nature [5]. In our early work [6], a variable capacitance diode of multilayer-nc-Si:H/c-Si heterojunction was prepared and a very high capacitance variable coefficient was demonstrated.…”