Effect of Ge Nanoislands on Lateral Photoconductivity of Ge-SiO_X-Si Structures

Abstract

The results of the experimental studies of the effect of nanoislands on the lateral photoconductivity in structures with Ge nanoislands formed on the SiOx layer using molecular beam epitaxy are reported. It is shown that nanoislands increase the surface recombination rate and affect the fundamental absorption edge of c-Si. The generation of lateral photocurrent in the range 0.8 – 1.0 eV was observed due to transitions between tails in the density of states of the near-surface c-Si, which is described by Urbach dependence. It was shown that the absorption spectrum of nanoislands is typical for the disordered Ge and is due to transitions between density-of-states tails of the valence and conductance bands. The mechanism is proposed of lateral photoconductivity involving the non-equilibrium charge carriers, generated in Ge nanoislands. It is suggested that the optical absorption and lateral photocurrent in Ge-SiOx-Si structures are affected by fluctuations of the surface potential in the near-surface region of c-Si, fluctuations of the Si band gap width and by effects of disorder in Ge nanoislands.

Surface reconstruction and optical absorption changes for Ge nanoclusters grown on chemically oxidized Si(1 0 0) surfaces

“…Urbach tail in PC spectra below band gap of Si (∼0.8-1.1 eV) may be caused by different kinds of uniformity in the underlying Si substrate. Moreover, this phenomenon has been observed in the previous work for structures with low density of Ge NCs [9].…”

“…where C is a constant, ε 0 is the width of the optical band gap. At excitement with quanta hv < ε 0 the Urbach tail is observed due to the crystal structure disorder [9]. Defects of crystalline structure of Ge can also give a contribution to absorption spectra and has an impact on threshold energy only and estimation of NC's band gap value.…”

“…Non-epitaxial Ge nanoislands which are separated from the substrate attract special interest due to spatial separation of electron-hole pairs leading to reduction of recombination rate [9]. NI's growth at the silicon surface covered with ultrathin silicon oxide layer is mainly determined by the dynamics of changes of the SiO x film structure and physical properties during Ge deposition and is principally possible at temperatures below ∼400 • C, when the formation of voids in ultrathin SiO 2 films is suppressed [10].…”

Морфологія та оптичні властивості нанокластерів Ge на окисленій поверхні Si(001)

“…Особливий iнтерес викликають менш зв'язанi з пiдкладкою неепiтаксiальнi нанокластери Ge насамперед за рахунок ефективного просторового роздiлення електрон-дiркових пар гетеропереходом Ge/SiO 2 /Si i вiдповiдного зменшення темпу рекомбiнацiї [9]. Створення таких нанокластерiв Ge на поверхнi Si(001), що вiдокремленi вiд пiдкладки Si ультратонким шаром оксиду кремнiю, головним чином, визначається динамiкою змiни структури та фiзичних властивостей плiвки SiO x пiд час осадження Ge [10] i є принципово можливим при температурах T < 400 • C, коли на поверхнi SiO 2 не виникають вiльнi вiд окислу "вiкна" [10].…”

Physical Insights on Charge Transport Mechanism and the LF Noise Behavior in Oxidized Si Structures with Ge Nanoclusters

“…In this respect, the structures with Ge nanoclusters (Ge-NCs) were realized on the oxidized silicon substrate [1]. These structures demonstrated the enhanced optical absorption and photoresponse [2]. The attractive properties of these structures result from the spatial quantization that can be attained for the structures with high-density NCs arrays and shrinking size of the separate NC down to 10 nm [3,4].…”