Abstract:Temperature induced changes of the local chemical structure of bulk amorphous GexSiOy are studied by Ge K-edge x-ray absorption near-edge spectroscopy and Si L2/3-edge x-ray Raman scattering spectroscopy. Different processes are revealed which lead to formation of Ge regions embedded in a Si oxide matrix due to different initial structures of as-prepared samples, depending on their Ge/Si/O ratio and temperature treatment, eventually resulting in the occurrence of nanocrystals. Here, disproportionation of GeOx … Show more
“…The sample deposited at 500 °C is different, so almost whole amount of Ge is oxidized (the curve of oxidized Ge is very close to that of total Ge) and the concentration of oxidized Ge (together with total Ge) decreases from the film/Si interface to the free surface of the film. This suggests that a part of Ge is lost, even during film deposition at higher temperature by formation of GeO 36,38–40 that is described by following reactions: (i) phase separation by GeO x → Ge + GeO 2 or by reduction of Ge oxides by Si or Si sub-oxides via GeO x + SiO y → Ge + GeO x − z + SiO y + z (this reaction starts at 300 °C) and then (ii) Ge loss by reaction GeO 2 (solid) + Ge(solid) → GeO(gas) (this becomes dominant at temperature over 400 °C 38,39,41 .Figure 3Atomic concentration dependence on the film thickness, for films deposited at ( a ) 300 °C and ( b ) 500 °C. The concentrations were obtained from XPS measurements, namely O 1 s, Ge 3p and Si 2p lines.…”
In this work we prepared films of amorphous germanium nanoparticles embedded in SiO
2
deposited by magnetron sputtering on Si and quartz heated substrates at 300, 400 and 500 °C. Structure, morphology, optical, electrical and photoconduction properties of all films were investigated. The Ge concentration in the depth of the films is strongly dependent on the deposition temperature. In the films deposited at 300 °C, the Ge content is constant in the depth, while films deposited at 500 °C show a significant decrease of Ge content from interface of the film with substrate towards the film free surface. From the absorption curves we obtained the Ge band gap of 1.39 eV for 300 °C deposited films and 1.44 eV for the films deposited at 500 °C. The photocurrents are higher with more than one order of magnitude than the dark ones. The photocurrent spectra present different cutoff wavelengths depending on the deposition temperature, i.e. 1325 nm for 300 °C and 1267 nm for 500 °C. These films present good responsivities of 2.42 AW
−1
(52
μ
W incident power) at 300 °C and 0.69 AW
−1
(57 mW) at 500 °C and high internal quantum efficiency of ∼445% for 300 °C and ∼118% for 500 °C.
“…The sample deposited at 500 °C is different, so almost whole amount of Ge is oxidized (the curve of oxidized Ge is very close to that of total Ge) and the concentration of oxidized Ge (together with total Ge) decreases from the film/Si interface to the free surface of the film. This suggests that a part of Ge is lost, even during film deposition at higher temperature by formation of GeO 36,38–40 that is described by following reactions: (i) phase separation by GeO x → Ge + GeO 2 or by reduction of Ge oxides by Si or Si sub-oxides via GeO x + SiO y → Ge + GeO x − z + SiO y + z (this reaction starts at 300 °C) and then (ii) Ge loss by reaction GeO 2 (solid) + Ge(solid) → GeO(gas) (this becomes dominant at temperature over 400 °C 38,39,41 .Figure 3Atomic concentration dependence on the film thickness, for films deposited at ( a ) 300 °C and ( b ) 500 °C. The concentrations were obtained from XPS measurements, namely O 1 s, Ge 3p and Si 2p lines.…”
In this work we prepared films of amorphous germanium nanoparticles embedded in SiO
2
deposited by magnetron sputtering on Si and quartz heated substrates at 300, 400 and 500 °C. Structure, morphology, optical, electrical and photoconduction properties of all films were investigated. The Ge concentration in the depth of the films is strongly dependent on the deposition temperature. In the films deposited at 300 °C, the Ge content is constant in the depth, while films deposited at 500 °C show a significant decrease of Ge content from interface of the film with substrate towards the film free surface. From the absorption curves we obtained the Ge band gap of 1.39 eV for 300 °C deposited films and 1.44 eV for the films deposited at 500 °C. The photocurrents are higher with more than one order of magnitude than the dark ones. The photocurrent spectra present different cutoff wavelengths depending on the deposition temperature, i.e. 1325 nm for 300 °C and 1267 nm for 500 °C. These films present good responsivities of 2.42 AW
−1
(52
μ
W incident power) at 300 °C and 0.69 AW
−1
(57 mW) at 500 °C and high internal quantum efficiency of ∼445% for 300 °C and ∼118% for 500 °C.
“…It is known that the chemical reduction of GeO x plays an important role and represents the major mechanism to produce size-controlled Ge-nps, embedded into a dielectric matrix of stoichiometric SiO 2 . This determines the dark current level (which should be as small as possible) whereas Ge:SiO x layers with small oxygen deficit ( x < 2) represent the favorable components for photovoltaic applications, according to the analysis conducted by A. Nyrow and co-workers [35]. This approach is reported also in the research led by W. Little et al which assigns the light emission in Ge-nps to the presence of oxygen-terminated nanoparticles [36].…”
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.
“…Вследствие своей непрямозонной структуры объемный германий (Ge) не может излучать свет с высокой эффективностью. Исследователи пытаются использовать ряд подходов для преодоления этого фундаментального ограничения, такие как смягчение правил отбора по квазиимпульсу в квантоворазмерных нанокластерах [4][5][6][7]; приложение деформаций, изменяющих зонную струк-туру [8][9][10]; создание светоизлучающих дефектов [11][12][13]; создание наночастиц Ge x Si 1−x [14][15][16][17][18][19][20]. В то время как нанокристаллы (НК) кремния хорошо изучены, НК Ge изучались не столь интенсивно, хотя они обладают преимуществами.…”
The non-stoichiometric germanosilicate films of two types GeOx[SiO](1-x) and GeOx [SiO2](1-x) were obtained by high-vacuum evaporation of GeO2 and either SiO or SiO2 powders and sputtering on a cold Si (001) substrate. The as-deposited and annealed (550 and 650 oC, 1 hour) samples were studied by IR spectrocopy, electron microscopy, Raman spectroscopy and photoluminescence (PL). From an analysis of Raman spectra, it was found that the as-deposited GeO[SiO2] film did not contain germanium clusters, and the as-deposited GeO[SiO] film contained amorphous germanium clusters; according to electron microscopy, it’s size was ~3 nm. According to IR spectroscopy, the films contained Si-O, Ge-O, and Si-O-Ge bonds. After annealing at 550 °C, amorphous germanium clusters were detected in both films, and after annealing at 650 °C, germanium nanocrystals were observed. A wide PL band with a maximum of 1050 nm was found in the as-deposited films at low temperatures. PL is probably due to defects, presumably oxygen vacancies and excess germanium atoms. Annealing causes a transformation of both film structure and PL spectra. In films containing germanium nanoclusters, PL is observed with a maximum of 1500–1600 nm. In this case, the PL signal from defects decreased. The temperature dependence of the intensity of the PL peaks was studied; it decreased with increasing temperature but remained at temperatures up to 200 K. The contribution to the PL from germanium nanocrystals formed during annealing is discussed.
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