Photoconductivity of structures nanodimensional Ge/c-Si

Abstract

Ruslana S. Udovitskaya, Sergey V. Kondratenko, Oleg V. Vakulenko Department of Physics, Taras Shevchenko Kyiv National University Prosp. Acad. Glushkova, 6, Kyiv 03127, Ukraine; tel/f ax: +38044 266 2296/2664507; e-mail: rusya@.univ.kiev.ua ]Abstract The spectral dependence of photoconductivity of struct ure nanodimensional Ge/c-Si was measured on infrared spectrophotometer DCS-12 which contains Ge quantum ho les on a surface of single-crystal substrate. The photoconductivity spectrum of nanodimensional Ge / c-S i structure was received at room temperature. The investigated samples are made by molecular - beam epitaxy method, rectan gular frame type (5x5 micron) contact was generated on a surface of Ge layer. The thickness of a contact strip was equaled to 0,5 micron. The second contact was soldered to the back side of the singlecrystal surface. A shifting voltage of U =1,5 V was switched in the opposite direction (negative potential to Ge slice) At measurements of photoconductivity of structure. It is necessary to note that photoconductive signal was 3 orders less, than at inverse displacement. It sp ecifies presence heterotransitions between Ge and c-S i layer. The photosensitivity of a standard s ilicon photodiode was investigated for comparison of such assumption. For example the spectral dependence of photos ensitivity of standard silicon photodiode N< -142 D is represented. The spectral position of a photoconductivity curve was the same to standard silicon photodiode at room temperature. The value of photosensitivity of a researched sample was compared with the standard photodiode. Is established, that both these values are of the same order. It is possible to explain it by presence of a potential barrier between Ge and Si. It is known that longwave border of photoconductivity is defined by width of the forbidden zone of the semiconductor. The increase of photocondu ctivity is caused by increase of absorptio n at rising of quantums energy of the exited radiation (at reduction of wavelength). The form of a photoconductivity spectrum of the photodiode N< -142 D and absence of a hole in the spectrum in short-wave area (1,5-2,1 micron) specifies that the speed of a surface recombination is equal to zero. For the structure nanodimensional Ge/ c-S i, otherwice, significant hole in this area was observed at the room temperature. So, samples had the large speed of surface recombination. To observe the contribution of nonequilibrium charge carriers to the photoconductivity of structure nanodimensional Ge / c-S i it is necessary to cool down to L < 100 D . The intersubband transitions can occur in nan odimensional Ge at such temperatures. So, it is necessary to expect observation of a phot osensitivity in the infrared, which corresp onds energy of these transitions. It is possible to explain photosensitiv ity of nanostructures by existence of inte rzoned transitions in nanodimension Ge. The spectral dependence of photosensitivity of structure nanodimensional Ge/c-S i in IR- of area is received. Keywords: photoconductivity, nanodi mensional, infrared Introduction Works with creation of receivers of radiation with quantum holes began only at the end of 90th years basically on a basis heterostructures InAs/GaAs and Ge/S i, and at present while all efforts are concentrated on reception effect's single elements. Photodetectors with quantum holes in a condition to cover an essential part infrared range, actual for many uses, since TV communications lengths of waves in near IR ar eas (1.3-1.5 microns) and finishing distant IR with a range of a spectrum (20-200 microns). Additional restriction of movement of carriers of a charge in surfaces of structures, and also a discrete power spectrum of carriers of a charge results in a lin e of essential advantages of photodetectors with quantum holes in comparison with structures with quantum points, and also with volumet ric spheres. Creation of new photodetectors with use quantum effects, demands deep understanding of physics of nonequilibrium processes in nano dimensional structures. Informative me thod of the analysis of course of none quilibrium processes are photo-electric methods . Therefore the purpose of our work there was to find out the nature of a photosensitive structures Germany - on-Silicon. In work it has been measured spectral dependence of photoconductivity of nano dimensional structures with Ge/c-Si. Comparison of the received resu lts with spectra of a photo sensitive standard silicon photo diodes is carried out. It is established, that structures with nano dimensional Ge /c-Si a photo are sensitive in infra-red area (1-3 microns) at low temperatures (77K). The photosensitive, such nano structures are caused between subzone by transitions nano dimensional in Ge.