Enhanced photoresponse of Ge/Si nanostructures by combining amorphous silicon deposition and annealing

Abstract

In order to inhibit high carrier recombination rates in Ge-on-Si nanostructures, GexSi1–x nanoislands were covered by a thin amorphous silicon layer via a low pressure CVD process. It is demonstrated that the surface photovoltage (SPV) signal in capped GexSi1–x/Si is increased by an order of magnitude compared to that of bare GexSi1–x islands, which can be due to the effective passivation of recombination centers at the a-Si/GexSi1–x interface. The effect is even more enhanced after subsequent annealing at 400 °C in an O2 ambient environment, with the signal increases ranging from 5 to 10 times. The observed increased photovoltage is accompanied by longer time decays in the SPV transients, being most increased after the annealing step. These results show that the photoexcited electron-hole pairs can be efficiently separated by the internal electric field at the a-Si/GexSi1–x/c-Si interfaces and can contribute to the photovoltage with decreasing recombination in GexSi1–x islands or at the interfaces. This work can facilitate the photovoltaic applications of Ge/Si heterostructures.

Frequency-Dependent Sonochemical Processing of Silicon Surfaces in Tetrahydrofuran Studied by Surface Photovoltage Transients

“…Following the analysis given elsewhere [ 49 , 50 ], a stretched-exponent decay model was used here, so that the SPV signal is described by: where is the characteristic stretched-exponent decay time and is the dispersion factor, which describes the spread of time constants. Obviously, 1 for a monoexponential decay, whereas the values describe a variation from a monoexponential decay with smaller values corresponding to a broader distribution of decay times.…”

Ultrasonic Processing of Si and SiGe for Photovoltaic Applications

“…Using an amorphous silicon layer should also prove useful in Ge x Si 1-x /Si structures [27]. It is seen in Figure 1 that the surface photovoltage (SPV) is enhanced as the structure is covered with a-Si (curves 3 and 4 compared with curves 1 and 2 at time t ¼ 0).…”

Tailoring Surface Self‐Organization for Nanoscale Polygonal Morphology on Germanium

“…Controlled and periodic germanium nanostructures exhibit significant applications in lasing, [1,2] infrared surface plasmon based molecular sensing, [3,4] surface-enhanced infrared absorption spectroscopy, [5,6] photovoltaic, [7,8] as photodetectors in optoelectronics, [9,10] enhanced light trapping, [3,11] and terahertz The occurrence of ordered arrays of objects or ordered morphological features, is a widely seen phenomenon in nature known as self-organization, straddling from ripples on sand dunes to leaf venation through molecular and atomic arrangements on the surfaces and in materials. [15] Inspired by such natural occurrences, self-organization phenomena such as preferred particles assemblies on the textured surfaces, straininduced pattern formation by surface relaxation, and energy beam induced nanopatterning by self-organization of the surface atoms are common strategies for the formation of nanoscale structures.…”

“…[3,4] Arrays of GeSi nanostructures on silicon substrate showed an enhancement in the photo-voltage, showing promise for solar cell applications. [10] Surprisingly, germanium being an indirect bandgap semiconductor, periodic arrays of germanium nanostructures gave rise to THz radiation emission with comparable amplitude to the direct bandgap semiconductor n-GaAs (n-type GaAs). [13] Germanium nanostructures show threefold to fivefold increased amplitude of THz radiation emission as compared to the baregermanium surface.…”