Temperature dependence of hopping‐edge in amorphous hydrogenated silicon

Abstract

Luminescence peak energy of amorphous hydrogenated silicon (a‐Si:H) increases with excitation energy in the Urbach tail and in the higher excitation energy range the peak energy is constant. The excitation energy at which the peak energy turns from increase to constant is shown to be understood as the hopping‐gap. The hopping‐gap decreases with temperature as in the case of the optical bandgap. Furthermore, it is discussed by comparing with the luminescence in porous Si that the luminescence in a‐Si:H may be due to the radiative recombination of electron‐hole pairs in hydrogen‐free Si nanostructures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Luminescence from hydrogen‐free silicon nanostructures in amorphous hydrogenated silicon

“…3 [16,17]. This shows that the hopping-gap in the a-Si:H film A at 15 K is 1.52 eV [16,17]. The pairs created directly at the localized band tail states in the hopping-gap by the excitation light less than 1.52 eV, recombine there without the hopping relaxation for the low density of the localized band tail states as shown in Fig.…”

“…This shows that the hopping-gap in the aSi:H film D is 1.7 eV. It should be noticed that these hopping-gaps of 1.52 and 1.7 eV obtained are in the Urbach tail region [16,17].…”

“…It is explained that electron-hole pairs excited by the excitation light higher than 1.52 eV reach the hopping-edges of the conduction and valence bands by the hopping energy relaxation at localized band tail states and then radiatively recombine at the edges as shown in Fig. 3 [16,17]. This shows that the hopping-gap in the a-Si:H film A at 15 K is 1.52 eV [16,17].…”

“…2 Experimental The a-Si:H films of a thickness of 1~3 μm were deposited on quartz substrates with rough surfaces kept at 250, 200, 180 and 150 °C by the ordinary rf glow discharge decomposition method of a SiH 4 [16,17]. The a-Si:H film of a thickness of ~2 μm was deposited on quartz substrates with rough surfaces kept at 250 °C by the ordinary rf glow discharge decomposition method of a SiH 4 (10 % in H 2 ) gas for the observation of the luminescence accompanying with phonon emissions.…”

Electron hopping‐randomwalk at localized band tail states with exponential density in amorphous hydrogenated silicon

“…Let us name the energy difference between the hopping-edges of electrons and holes the hopping-gap [7]. The hopping-gap is obtained from the excitation energy dependence of the luminescence peak energy in a-Si:H [7,10]. The hopping-gap obtained from the dependence decreases with increasing temperature as shown in Fig.…”