Studies On Amorphous Ⅲ-V Semiconductor Films For Detectors Application

Ⅲ-Ⅴcrystalline materials have attracted widespread attention because of its better thermal stability,higher absorption coefficient,higher carrier mobility and possibility of application at room temperature.Compared withⅢ-Ⅴcrystalline semiconductors, amorphous semiconductors have some attractive characters such as low cost and easy preparation process.MoreoverⅢ-Ⅴamorphous materials keep semiconductor properties, led to their potential applications in future detectors(application band:1～3μm) and other optoelectronic devices.But amorphousⅢ-Ⅴsemiconductors are still lack of systematic and detailed study.In this paper,our study on amorphous(a-) In_xGa_1-xAs and a-InSb films includes the preparation,characterization,annealing and hydrogen passivation.Main contents are as follows:1.The preparation process of amorphousⅢ-ⅤfilmsAmorphousⅢ-Ⅴfilms are deposited on substrates of glass and silicon by RF magnetron sputtering technique.Based on the studies of material growth mechanism and kinetics analysis,we analyze the effects of sputtering parameters on the structure of film.In order to prepare amorphous films,we must reduce the energy of sputtering particle by means of decreasing sputtering power P_rf,lowering substrate temperature T_S or increasing working pressure P_w.Through many experiments,we have obtained"growth window"used for a-In_xGa_1-xAs and a-InSb films.The conclusions are summarized as follows:(1)When P_w is in the range of 0.5-8 Pa,we obtain a-GaAs film with T_S of 20℃and P_rf of 40-100 W.(2)For each value of T_S,the results of InAs films show the existence of a threshold value of P_w.The films are amorphous above threshold value and the films are polycrystal below threshold value.This threshold value of P_w also increases with increasing P_rf.(3)We have deposited a-In_xGa_1-xAs films by changing RF power of GaAs target and RF power of InAs target.(4) At T_S=20℃,we obtain a-InSb films when P_rf is 50W and P_w is higher than 3 Pa.2.The characterization of amorphousⅢ-ⅤfilmsWe have characterized structure,surface morphology and composition of amorphous films by means of X-ray diffractometer(XRD),transmission electron microscopy(TEM), scanning electron microscopy(SEM) and electron diffraction spectroscopy(EDS).Through the systematical study the effect of sputtering parameter on the structure,surface morphology and composition,we have prepare stoichiometric amorphous films with better surface morphology.And we calculate the radical distribution function and pair correlation function from XRD in order to obtain microstructure data of a-In_xGa_1-xAs thin films.For a-GaAs and a-InAs films,coordination numbers of the first neighbouring atoms is smaller than 4 due to the presence of wrong bonds in films.The radical distribution function of a-InGaAs separates two peaks at 2.58(?) and 2.7(?),respectively.We assign them to Ga-As band and In-As band.With the content of In increasing,the intensity of the peak at 2.5 8(?) decrases and the peak at 2.7(?) changes reversely.We characterize the optical properties of a-In_xGa_1-xAs and a-InSb thin films by spectrophotometer and the ellipsometry.We have investigated how process parameters influence the optical band gap of amorphous semiconductors.Experimentally,it is found that optical band gap broadens with increasing P_w or decreasing P_rf because the breadth of band tail reduces.The optical band gap of a-In_xGa_1-xAs films shifts from 0.72eV to 1.77 eV.And optical gap of a-InSb is in the range of 0.462-0.61eV.But we don't find the definite relation between optical band gap and In content for a-In_xGa_1-xAs films.We obtain optical constants of thin films from ellipsometry.The optical constants of amorphous films show enormous differences from polycrystal films and monocrystal films.We study the electrical properties of thin films using Hall system.The results suggest greater levels of disorder leads to smaller carrier concentration and larger resistivity. a-In_xGa_1-xAs and a-InSb thin films have obvious photosensitive properties at light.The photo sensitivity increases with increasing working pressure for the case of a-GaAs.We have found the similar trend in a-InSb.But the photo sensitivity is only obvious in the stoichiometric a-InAs film.Compared with photo sensitivity in a-GaAs and A-InSb,the value in a-InAs is smaller.3.The study on annealing of amorphous a-In_xGa_1-xAs filmsWe have carried out annealing experiments.The experiment results show crystallization temperature of a-In_xGa_1-xAs films is about 300℃.We have observed the optical gap shifts to higher energies as annealing temperature is below crystallization temperature.We propose that these changes are due to a diminution of the tail state defects and/or the relaxation of strained bonds.When annealing temperature is higher than crystallization temperature,the optical gap decreases.And the the breadth of band tail increases due to an increase of the number of distorted and broken bonds in the interface between the crystalline clusters and the amorphous matrix.Moreover we have found H releases from a-In_xGa_1-xAs films and photo sensitivity decreases while annealing.4.The study on amorphousⅢ-Ⅴfilms doping hydrogenWe investigate the passivation of hydrogen on the amorphousⅢ-Ⅴfilms.Hydrogen induces blue shifts in absorption edge and increasing of photoconductivity.We also have found doped hydrogen results in crystallization for a-InAs films. In summary,we have depositedⅢ-Ⅴamorphous films by RF magnetron sputtering. Moreover we have investigated the effects of sputtering parameters on the structure,surface morphology,composition and properties.We can obtainⅢ-Ⅴamorphous films for detector through optimizing deposited conditions.Our study provides practical experience for their potential applications in future detectors.