Photoconductivity of structures nanodimensional Ge/c-Si

摘要

The spectral dependence of photoconductivity of structure nanodimensional Ge/c-Si was measured on infrared spectrophotometer DCS-12 which contains Ge quantum holes on a surface of single-crystal substrate. The photoconductivity spectrum of nanodimensional Ge/c-Si structure was received at room temperature. The investigated samples are made by molecular-beam epitaxy method, rectangular 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 specifies presence heterotransitions between Ge and c-Si layer. The photosensitivity of a standard silicon photodiode was investigated for comparison of such assumption. For example the spectral dependence of photosensitivity of standard silicon photodiode ΦB-142K 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 photoconductivity is caused by increase of absorption at rising of quantums energy of the exited radiation (at reduction of wavelength). The form of a photoconductivity spectrum of the photodiode ΦB-142K 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-Si, otherwise, 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-Si it is necessary to cool down to T < 100 Κ. The intersubband transitions can occur in nanodimensional Ge at such temperatures. So, it is necessary to expect observation of a photosensitivity in the infrared, which corresponds energy of these transitions. It is possible to explain photosensitivity of nanostructures by existence of interzoned transitions in nanodimension Ge. The spectral dependence of photosensitivity of structure nanodimensional Ge/c-Si in IR- of area is received.