Minority-carrier diffusion length, minority-carrier lifetime, and photoresponsivity of β-FeSi2 layers grown by molecular-beam epitaxy

Abstract

We have epitaxially grown undoped b-FeSi 2 films on Si(111) substrates via atomic-hydrogen-assisted molecular-beam epitaxy. b-FeSi 2 films grown without atomic hydrogen exhibited p-type conduction with a hole density of over 10 19 cm À3 at room temperature (RT). In contrast, those prepared with atomic hydrogen showed n-type conduction and had a residual electron density that was more than two orders of magnitude lower than the hole density of films grown without atomic hydrogen (of the order of 10 16 cm À3 at RT). The minority-carrier diffusion length was estimated to be approximately 16 lm using an electron-beam-induced current technique; this value is twice as large as that for b-FeSi 2 prepared without atomic hydrogen. This result could be well explained in terms of the minority-carrier lifetimes measured by a microwave photoconductance decay technique. The 1/e decay time using a 904 nm laser pulse was approximately 17 ls, which is much longer than that for b-FeSi 2 prepared without atomic hydrogen (3 ls). The photoresponsivity reached 13 mA/W at 1.31 lm, which is the highest value ever reported for b-FeSi 2 films.

Synthesis and characterization of β-phase iron silicide nano-particles by chemical reduction

“…There has been increasing research on metal silicides during last few years [1][2][3][4][5] for its application in Schottky barriers, ohmic contacts, interface diffusion barriers and photovoltaics. While most of the silicides have good metallic properties there are very few having attractive semiconducting properties.…”

“…Though the diffusion length of minority carriers in ␤-FeSi 2 are moderate enough (10-100s of m depending on hole or electron concentration [4,5,13]), it is still much less than that of Si or other semiconducting materials. Therefore, the reported ␤-FeSi 2 emitter layer thickness has been taken as few ten to hundred nanometers to achieve maximum efficiency [2,[10][11][12].…”

“…Thereafter iron silicide nano-particle has been characterized extensively using XRD, FESEM, HRTEM, EDX, ultra-violet-visible absorption spectroscopy, Hall measurement to examine its structural character, morphology, purity, bandgap and other electronic properties like mobility, carrier concentration etc. 4 ] was added into the ferric nitrate solution. After that, the mixed solution was stirred at 1000 rpm for approximately 10-12 hrs to hydrolyse the orthosilicate in the presence of ammonium acetate which further resulted in sol-gel polymerization of tetraethyl orthosilicate [24].…”

“…Deionized water from Milli-pore purification system is used for the preparation of aqueous solution.2.2. Synthesis procedureThis synthesis technique of ␤-FeSi 2 was carried out by the chemical reaction between nona-hydrate ferric nitrate [Fe(NO 3 ) 3 , 9H 2 O] and tetraethyl orthosilicate [Si(OC 2 H 5 )4 ] where ferric nitrate acted as source for iron and tetraethyl orthosilicate acted as source for silicon. Their molar ratio was maintained at 1:2 for the formation of FeSi 2 .…”

Effect of atomic-hydrogen irradiation on reduction of residual carrier concentration in β-FeSi2 films grown on Si substrates by atomic-hydrogen-assisted molecular beam epitaxy

“…Terai et al achieved carrier concentrations of the order of 10 16 cm -3 by precisely controlling the growth conditions in molecular-beam epitaxy (MBE) [19]. Very recently, we successfully decreased the residual carrier concentrations by MBE using a cracking cell for generating atomic hydrogen [20]. The conduction type changed from p-to n-type and the carrier concentration was two orders of magnitude (of an order of n ≈ 10 16 cm -3 ) lower than that for films grown in the absence of atomic hydrogen.…”