Local characterization of electronic transport in microcrystalline silicon thin films with submicron resolution

Abstract

Two-dimensional maps of dark conductivity with submicron resolution have been obtained on in situ prepared hydrogenated microcrystalline silicon (μc-Si:H) layers used for solar cells by atomic force microscopy with conductive cantilever. Comparison of the morphology and current image allows clear identification of Si crystallites. Pronounced current decrease has been detected at the grain boundaries. The technique was used to study initial stages of μc-Si:H growth, and we show how the incubation layer, detrimental for solar cells efficiency, can be minimized by pulsed excimer laser crystallization of the initial amorphous layer.

Ultrafast carrier dynamics in undoped microcrystalline silicon

“…The mc-Si:H can be understood as composite of silicon crystallites with typical dimensions 10-100 nm in the a-Si:H host [4,8]. On this basis one could expect that the dynamics of excited carriers -to the first approximation -can be interpreted as a mixture of dynamics in c-Si and in a-Si:H with the relative weights corresponding to the ratio of relevant fractions.…”

“…The investigation of basic physical processes in this material is still in progress. In particular, the correlation between the structure and the optical and electrical properties of the material is studied by variety of experimental techniques [2][3][4][5][6][7][8]. Most often the correlation between the crystalline volume fraction and the material properties is investigated.…”

Some controversial points related to transport in microcrystalline silicon

“…In order to study the local electronic properties of the grains or columns in µc-Si:H, we have pioneered the use of AFM with a conductive cantilever as a probe of local conductivity [2]. Our first measurements were performed in the Omicron ultra-high vacuum (UHV) AFM on samples deposited in the attached chamber and transferred without breaking the vacuum in order to prevent surface oxidation.…”

“…In the following section we shall show that there is no conflict between our macroscopic conductivity [10][11][12][13][14] and microscopic C-AFM results [2], which was broadly discussed in [6].…”

“…On the basis of atomic force microscopy (AFM) combined with the local current mapping [2], electron spin resonance (ESR) [3,4] and many other techniques it is generally believed that µc-Si:H is actually composed of at least two characteristic sizes of crystalline Si grains: the small ones (10 -30 nm) and the large ones (100 -500 nm), formed as aggregates (columns) from the small ones.…”