Influence of microstructure and composition on hydrogenated silicon thin film properties for uncooled microbolometer applications

Abstract

Doped n-and p-type hydrogenated silicon (Si:H) thin films prepared by plasma enhanced chemical vapor deposition have been investigated for uncooled microbolometer applications. The material microstructure has been studied by in situ real time spectroscopic ellipsometry collected during thin film deposition or ex situ spectroscopic ellipsometry measurements on a static sample with a multiple sample analysis technique. The key electrical properties of interest, including film resistivity (q), temperature coefficient of resistance (TCR), and 1/f noise, have been measured as a function of deposition conditions for p-type amorphous hydrogenated silicon (a-Si:H) films and microcrystalline content for n-type amorphous (a), microcrystalline (lc), and mixed-phase amorphous þ microcrystalline (a þ lc) Si:H films. The TCR and 1/f noise values were compared for p-and n-type a-Si:H samples in the resistivity range of 100 < q < 3000 X cm and show that for a given resistivity, amorphous p-type films exhibit a lower 1/f noise, which might be expected due to a larger density of majority carriers. V

Electrical Activity of Boron and Phosphorus in Hydrogenated Amorphous Silicon

“…Resistivity reaches a maximum and then decreases with further dilution up to the onset of crystallinity [26]. Crystallite inclusions then result in additional decreases in resistivity, as expected due to the higher doping efficiency of impurities within a crystal lattice [21,23,26]. The initial increase in resistivity within the amorphous phase may be due to small amounts of hydrogen being incorporated into the network; however, not enough is present to generate B(3,1) or P(3,1) configurations and passivate nearby dangling bond defects.…”

“…[23,24]. Variations in resistivity with H 2 dilution have also been observed for both doping types [21,25,26]. Generally, material made at low-H 2 dilution remains amorphous throughout growth; however, sufficient dilution can result in the nucleation and subsequent growth of crystallites from the amorphous phase under appropriate conditions [27].…”

“…In Ref. [21], it is suggested that at low B concentration holes can be trapped at strained Si-Si bond centers [22]. The charge due to these trapped holes may be compensated by a H atom trapped in the bond centers.…”

“…The siliconhydrogen-bonding configuration (Si-H n , n ¼ 1, 2, 3) has also been linked to material electronic quality [28][29][30]. Larger-scale variations such as the formation of divacancies, nanoscale voids, and variations in overall film density have been detected in the infrared to visible range optical properties [21,[28][29][30][31]. Whenever hydrogen and impurity atoms are introduced jointly, there can be interplay between order induced among the silicon atoms in the network and the functionality of the dopant atoms.…”

Spectroscopic Ellipsometry Studies of n-i-p Hydrogenated Amorphous Silicon Based Photovoltaic Devices

“…The films used to develop growth evolution diagrams for doped and undoped Si:H deposited in the glass substrate/BR/ n - i - p a-Si:H device configuration were grown as a function of R in an effort to probe the subtle fluctuations expected as the material transitions from amorphous to nanocrystalline [ 31 , 55 ]. A distinct type of roughening transition is reported in which crystallites nucleate from the growing amorphous phase.…”