The Fabrication,Modeling And Application Of InGaZnO/Si Heterojunction Photodiodes

Potential applications of transparent oxides in optoelectronic devices have attracted much attention in recent years.Some researchers have studied the behavior of transparent oxide/Si heterostructure photodiode(short as PD)such as ZnO/Si photodiode,due to their high quantum ef:ficiency,fabrication method combined with CMOS fabrication method and good photoelectrical properties.In this paper,IGZO/Si heterojunction photodiodes(short as IGZO/Si PD)with both high quantum efficiency and low dark leakage current density were fabricated by RF magnetron deposition at 25 ?,200? and 400 ?,respectively.Since the IGZO/Si PDs inherented the instinct non-linear photoelectronic response that exists in most of the transparent oxide semiconductor/Si heterojunction PDs,a model considering interface states at IGZO/Si interface that based on experiment dataes is built to fit the dataes and to explain the reason of the non-linear photoelectronic response.And at last,the application of IGZO/Si heterojunction PD in activated pixel sensor is modeled according to the measured dataes.The effects of the deposition temperature,oxygen pressure and SiO2 buffer layers on ITO/IGZO/Si/Al heterojunction PD were studied,and most of photocurrents in this work are reflected in S-shaped I-V characteristics.All n-IGZO/p-Si PDs fabricated at 25 ?,200? and 400 ? exbhit good rectification characteristics higher than 1 × 103 and QE higher than 80%.With decreasing deposition temperature,using Ar2/O2 mixed atmosphere as deposition ambience or introducing SiO2 buffer layer,the dark leakage current density of IGZO/Si heterojunction PDs is decreased significantly.The characterization of IGZO films indicates that the band energy of achieved IGZO film is larger than 3.7eV,transparent percent of visible light higher than 80%,carrier concentration higher than 1.1 ×1O17 cm-3,mobility higher than 8 cm2V-1s-1 and with thickness of 120nm.Since the IGZO film fabricated at room temperature owns both great electronic and photo parameters that the IGZO/Si PD owns both high QE and low dark leakage current density.It is observed that the photocurrent-voltage charateristics of IGZO/Si heterojunction PD shows non-liear photoresponse that exists in lots of transparent oxide/Si heterojunction PDs.Photocurrent of IGZO/Si heterojunction PDs increases while the QE decreases with increasing the intensity of incident light and the photocurrent incrases with increasing the reverse bias voltage in the non-linear photoresponse area.And the photocurrent keeps increasing until the reverse voltage at IGZO/Si PD reachs certain value(Vsat).At first,the influence of interface layer on the dark I-V character of IGZO/Si PDs is discussed according to heterojunction electron tunneling model.It is indicated that the the negatively charged states at IL determine the partial voltage of space charge region of Si and IGZO and that of interface.And the state density and recombination rate of interface layer is calculated for the modeling construction and discussion of photo-electronic character of IGZO/Si PDs later in this paper,based on the dark I-V characteristics of IGZO/Si PD and heterojunction electron tunneling model.The I-V characteristics under illumination observed here,Vsat decreases with increasing deposition temperature,are similar to those of ZnO/Si PDs reported before but deviate from those derived from model neglecting interface states.Since it has been demonstrated that there is an amorphous oxide layer(?2.5 nm thick)formed at the transparent oxide/Si interface during deposition,a model of IGZO/Si PD with Si oxide IL is developed to account for these results,which is also suitable for other heterojunctions with IL.The photoelectric model of IGZO/Si heterojunction PD is achieved by solving the pason and current serious equation.It is conclude that the photoelectric model of IGZO/Si heterojunction PD could explain the photo I-V and C-V character of IGZO/Si heterojunction PD very well after compared lots of experiment dataes and calculation results.In our model,the photo-induced electrons to flow through the interface layer will,therefore,be captured by the interface states or blocked by interface layer and may recombine at interface layer or flow through the IGZO barrier to induce photocurrent.It is indicated that both the effective interface electron mobility and the negatively charged states at interface layer determine the recombination current and photocurrent as well as partial voltage,by which,the light I-V characteristic is determined.Based on the model of IGZO/Si heterojunction PD considering interface layer,the relationship between photoelectronic characteristics of transparent oxide/Si heterojunction PD and parameters such as interface state density,effective mobility of electrons at interface state,the constant charge density at interface layer,carrier density of substrate and transparent oxide film,the recombination rate at interface layer and the electronic affinity of transparent oxide is studied,respectively.And the results guide ways to adjust the non-linear photoresponse characteristic of transparent oxide/Si heterojunction PD at low reverse bias voltage.The current-voltage characteristics and capacitance-voltage characteristics were measured under various incident light powers(ILP),they and their effects on the application of IGZO/Si heterojunction in active pixel sensor(APS)as photodiode were studied.It is indicated that these effects directly affect the application of IGZO/Si PD in APS by decreasing the conversion gain under strong ILP.Since the the intensity of the noise equivalent power only shows slight change with increasing the intensity of incident light or decreasing power supply voltage,the minimum detectable ILP keeps constant while the maximum detectable ILP is enlarged.Due to the nonlinear photoresponsivity and C-2-V characteristic,IGZO/Si PD actually has higher DR and this advantage is much more significant as working under low power supply voltage than Si PD.The studies indicate that IGZO/Si PD shows better performances and more potentiality under low operation voltage than traditional Si PD as application in APS,which would leads to more flexible APS design.