Electrical And Optoelectronic Properties Of GeAs/MoS₂ And GeAs/F₁₆CuPc Heterojunction Devices

As a new type of heterojunction,Van der Waals heterojunction is constructed of two or more two-dimensional materials.By choosing appropriate two-dimensional materials and optimizing the energy band alignment at the interface,Van der Waals heterojunction devices exhibit novel physical properties and have good application prospects in the field of electronic and optoelectronic devices.High-performance infrared detectors based on two-dimensional materials have very important application prospects in the civil and aerospace fields.In recent years,two-dimensional material infrared detectors have focused on narrow-bandgap semiconductors,such as black phosphorus and As P,and much progress has been achieved.However,considering the instability of black phosphorus and As P,their applications in infrared detectors have been significantly limited.GeAs is a new p-type two-dimensional narrow bandgap semiconductor?0.6 eV?,which has excellent chemical stability,high carrier mobility,and has a rapid response to infrared light,making it suitable for infrared detectors.However,due to the high dark current of GeAs,its near infrared detector performance,especially specific detectivity,is relatively low.In this thesis,the Van der Waals heterojunction devices based on GeAs have been constructed to reduce its dark current and further improve its infrared light detection performance.In this thesis,the electrical and optoelectronic properties of GeAs heterojunction device have been studied.First,the GeAs,MoS₂,F₁₆CuPc field effect transistors?FETs?were constructed and the device performance was measured.The carrier mobility of GeAs can reach 18cm²V^-1s^-1;ON/OFF ratio of MoS₂ is 10⁶ respectively;the carrier mobility and ON/OFF ratio of F₁₆CuPc FET device are 0.52 cm²V^-1s^-1 and 10⁶,respectively.Through photoelectric measurement,it was observed that GeAs exhibited relatively weakresponse to light with wavelengths of 850 nm,1100nm,and 1550 nm.Among them,the light response coefficient R and specific detection ability D* at wavelength of 850 nm can reach 37A/W and 7×10¹⁰ Jones respectively.GeAs-MoS₂ inorganic-inorganic heterojunction device was constructed.By measuring the electrical properties of the device in the dark field,the device has obvious rectification characteristics,and the gate electric field can significantly modulate the rectification ratio of the heterojunction device.The maximum rectification ratio is 50.By measuring the transfer curve of the heterojunction device,it is found that the ON/OFF ratio of the device can reach up to 107.According to its output curves,compared to GeAs(V_g=-60 V and V_ds=0.1V,I_ds is 20?A),the current of the junction?GeAs-MoS₂?in the dark state is significantly reduced(V_g = 40 V and V_ds = 3V,I_ds is 0.9?A).From the optoelectronic measurements of the devices,the GeAs/MoS₂ heterojunction device exhibited response to the visible and near infrared light.The photoresponsivity?R?and specific detectivity?D*?at 650 nm and 1550 nm are 50A/W and 3.5×10¹² Jones,110 A/W and 8×10¹² Jones respectively.from the gate-dependent optoelectronic performance,it is found that the photoresponsivity and the specific detectivity increase with the increase of the gate voltage.This is because the positive gate bias increases the conduction and valence band offset between GeAs and MoS₂,leading to the larger driving force for the transfer of photogenerated electron sand holes,and the faster separation rate of photogenerated electron holes.The mechanism of photocurrent generation is that the photogenerated electrons on the GeAs conduction band move to the MoS₂ conduction band,and the photogenerated holes on the MoS₂ valence band also move to the valence band of GeAs,which can produce a certain amount photocurrent under the source-drain voltage.Organic materials can be used to make up for the shortcomings of less selectable materials and relatively high production costs of inorganic two-dimensional materials,and continue to exert their advantages of flexibility and high stability.Therefore,GeAs/F₁₆CuPc organic-inorganic heterojunctions can be introduced to reduce dark state current and improve light detection ability.By carrying out the electrical measurements of the junction,it is found that the reverse current of the output curve under the gate electric field is relatively large,and there is no rectification characteristic.This is because GeAs and F₁₆CuPc constitute a Type-? heterojunction: Under the reverse current,the electrons in the conduction band of F₁₆CuPc tunnel to the valence band of F₁₆CuPc,which increases the reverse current.By measuring the optoelectronic properties of the heterojunction,it is found that the heterojunction device presents an obvious photoelectric response at 850 nm with photoresponsivity of 25A/W and specific detectivity of 1.5×10¹⁴ Jones,respectively.According to gate-dependent band alignment of the junction,the photocurrent generation mechanism is that the photogenerated electrons on the conduction band of GeAs move to the HOMO of F₁₆CuPc,and the photogenerated holes on the F₁₆CuPc LOMO also move to the valence band of GeAs,leading to the photocurrent generation.By measuring the optoelectronic performance of the device under the light wavelengths of 1200 nm and 1550 nm,it was observed that the source-drain current of the device gradually decreased with the increase of light time and light power density.Through multiple measurements,the repeatability of this phenomenon was further confirmed.