Structural, optical, and electrical characterization of improved amorphous hydrogenated germanium

摘要

Highhyphen;quality amorphous hydrogenated germanium has been deposited using the diode rf glow discharge method out of a gas plasma of GeH4and H2. The optical, electrical, and structural properties of this material have been extensively characterized. The optical and electrical properties are all consistent with material containing a low density of defect related states in the energy gap. In particular, this material has an eegr;mgr;tgr;=3.2times;10minus;7cm2/V, ratio of photocurrent to dark current of 1.3times;10minus;1, and flux dependence of the photocurrent with ggr;=0.79 at 1.25 eV measured using photoconductivity, a mgr;tgr;=4times;10minus;8cm2/V measured using time of flight, an Urbach energy of 51 meV and agr; at 0.7 eV of 8.3 cmminus;1measured using photothermal deflection spectroscopy, a dangling bond spin density of 5times;1016cmminus;3measured using electron spin resonance, photoluminescence with a peak energy position of 0.81 eV and full width at half maximum of 0.19 eV, an activation energy of 0.52 eV and sgr;0of 6.1times;103(OHgr;thinsp;cm)minus;1measured using dark conductivity, and anE04band gap of 1.24 eV measured by optical absorption. The structural measurements indicate a homogeneous material lacking any island/tissue and columnar structure when investigated using transmission and scanning electron microscopy, respectively. Hydrogen concentrations calculated from infrared and gas evolution measurements can only by reconciled by postulating a large quantity of unbonded hydrogen whose presence is confirmed using deuteron magnetic resonance. The bonded deuterium component, as seen in this film using DMR, has a spinhyphen;lattice relaxation time of the order of 4000 s. The differential scanning calorimetry measurement shows crystallization occurring at 421thinsp;deg;C and the presence of large compressive stresses has been confirmed using a bendinghyphen;beam method. The experimental details necessary to interpret the quantities quoted here are set out in the text which follows. It is considered that the very good optical and electrical properties of this as yet unoptimized material are directly related to the structural properties detailed above.