Nanostructured germanium deposited on heated substrates with enhanced photoelectric properties

Abstract

SummaryObtaining high-quality materials, based on nanocrystals, at low temperatures is one of the current challenges for opening new paths in improving and developing functional devices in nanoscale electronics and optoelectronics. Here we report a detailed investigation of the optimization of parameters for the in situ synthesis of thin films with high Ge content (50 %) into SiO2. Crystalline Ge nanoparticles were directly formed during co-deposition of SiO2 and Ge on substrates at 300, 400 and 500 °C. Using this approach, effects related to Ge–Ge spacing are emphasized through a significant improvement of the spatial distribution of the Ge nanoparticles and by avoiding multi-step fabrication processes or Ge loss. The influence of the preparation conditions on structural, electrical and optical properties of the fabricated nanostructures was studied by X-ray diffraction, transmission electron microscopy, electrical measurements in dark or under illumination and response time investigations. Finally, we demonstrate the feasibility of the procedure by the means of an Al/n-Si/Ge:SiO2/ITO photodetector test structure. The structures, investigated at room temperature, show superior performance, high photoresponse gain, high responsivity (about 7 AW−1), fast response time (0.5 µs at 4 kHz) and great optoelectronic conversion efficiency of 900% in a wide operation bandwidth, from 450 to 1300 nm. The obtained photoresponse gain and the spectral width are attributed mainly to the high Ge content packed into a SiO2 matrix showing the direct connection between synthesis and optical properties of the tested nanostructures. Our deposition approach put in evidence the great potential of Ge nanoparticles embedded in a SiO2 matrix for hybrid integration, as they may be employed in structures and devices individually or with other materials, hence the possibility of fabricating various heterojunctions on Si, glass or flexible substrates for future development of Si-based integrated optoelectronics.

Ge nanoparticles in SiO2 for near infrared photodetectors with high performance

“…So, Ge-NPs are formed at about 310 °C 30 in indium tin oxide (ITO), in the range of 800–1000 °C 31,32 in Al 2 O 3 or above 700 °C in ZrO 2 matrices 33 . Structures based on Ge-NPs deposited on glass or flexible substrates can be obtained using or not a thermal treatment during the deposition process 34–36 .…”

Rapid thermal annealing for high-quality ITO thin films deposited by radio-frequency magnetron sputtering

“…Thin oxide films, used as contact electrodes [1–4], are considered to be important components of photovoltaic cells [5–6]. As an electrode candidate for solar cells, an ITO film [7–8] must present excellent optical and electrical properties for increased energy generation. At this time, the goal is to obtain high-performance solar cells [6,9–10] but at a cost as low as possible.…”

“…Due to these features, ITO films are promising components for the development of high-performance optoelectronics [7,11–13] and photovoltaic devices. In order to use ITO thin films for photovoltaic applications, samples with reproducible properties are required [8,14]. The performance of ITO in various applications increases when the electrical properties are improved.…”

SiGe nanocrystals in SiO2 with high photosensitivity from visible to short-wave infrared

“…For obtaining SiGe films or multilayers with targeted electric and photoelectric properties, different deposition methods as magnetron sputtering 2 , plasma enhanced chemical vapor deposition 13 , implantation 31 or evaporation 32 are used. The process of NCs formation in an oxide matrix is related with the deposition conditions if the deposition takes place on heated substrate [33][34][35] , but the films nanocrystallization can be accomplished by thermal annealing at suitable temperatures. For obtaining SiGe NCs in thin films or multilayers, annealing in 600-1055 °C range is performed 2,33,36,37 .…”

“…The process of NCs formation in an oxide matrix is related with the deposition conditions if the deposition takes place on heated substrate [33][34][35] , but the films nanocrystallization can be accomplished by thermal annealing at suitable temperatures. For obtaining SiGe NCs in thin films or multilayers, annealing in 600-1055 °C range is performed 2,33,36,37 . A challenging problem to form SiGe NCS in SiO 2 matrix is the oxygen excess that may occur during deposition process or heating treatment.…”