The EC-V Characterization Of â…¢-V Semiconductors And The Persistent Photocurrent Research Of GaN Based Photoconductive Devices

III-V compound semiconductors with direct bandgap have been widely used inthe field of photodector. Due to inert chemical property, direct and wide tunablebandgap, GaN-based materials have a wide application in high power, highfrequency electronic devices, light emitting diodes and ultraviolet photodetectors.Moreover, GaN-based ultraviolet photodetector has sharp and tunable response inthe ultraviolet band less than365nm, and its response wavelength range from365nmto200nm. And GaN-based ultraviolet photodetector can detect the radiation of solarblind band without the influence of long-wavelength radiation. Therefore,GaN-based ultraviolet photodetector has become an important direction ofultraviolet photodetectors. However, GaN-based photoconductive devices havepersistent photoconductivity because of the high concentration of deep level defectsin GaN-based thin-film materials, and the persistent photoconductivity prevents theapplication of GaN-based photoconductive devices. Meanwhile, among thematerials used for short wave infrared detectors, InGaAs has been widely usedbecause of excellent material properties and mature epitaxial technology. Sincedoping concentration is one of the key factors, which decide the performance ofsemiconductor devices. This paper firstly introduced the characterization the carrierconcentration of InP-based and GaN-based materials through ElectrochemicalCapacitance-Voltage method. Then we designed the GaN-based superlattice material,which is used to made GaN-based solar blind ultraviolet photoconductive detectors.Finally, we made a detailed study in the persistent photoconductivity of GaN basedsolar blind ultraviolet photoconductive detectors, which is made of GaN-basedsuperlattice material.Firstly, we characterized the vertical distribution of carrier concentration inInP-based and GaN-based materials through Electrochemical Capacitance-Voltagemethod. We found that there were errors when multilayer materials being measured:the thickness of every layer do not conform with the designed thickness, and thecarrier concentrations of every layer do not conform with the designed carrierconcentrations, especially when the carrier concentration ranges from high to low. Inorder to characterize the vertical distribution of carrier concentration insemiconductor materials correctly, we used SCM and SKPM to measure thematerials, and we got the correct thickness of every layer, but we can’t get an exact value of the carrier concentration in every layer. Then we tried to etch the surfacelayer after the measurement to surface layer was done, and we got the value of thecarrier concentration in every layer. So we got the relative accurate characterizationof semiconductor materials.Secondly, we made a research on the origin of the persistentphotoconductivity in GaN-based photoconductive devices，then we made an analysison the persistent photoconductivity research at home and abroad. We designed theGaN-based superlattice material, which is used to made photoconductive device.The superlattice layer consists of two kinds of AlxGa1-xN with different compositionof Al: Al0.65Ga0.35N and Al0.42Ga0.58N, each layer has a thickness of5nm, there are20periods totally. We made transmission spectra measurement on the GaN-basedsuperlattice material. From the result of transmission spectra, we can tell that theabsorption edge of the material locates at the solar blind band.Finally, we made GaN-based solar blind ultraviolet photoconductive deviceand made a measurement of its response spectrum, we found that thisphotoconductive device responds at solar blind band, and had a highest responsivityat245nm. Then we made a detailed study of electric field effects and thermal effectson the persistent photoconductivity of GaN-based superlattice photoconductivedevice. We found that adding a high bias voltage during the decay of persistentphotoconductivity can make the current drop to a low value, which is lower than theoriginal current. And the higher and longer of the bias voltage, the current declineslower. Meanwhile, the higher the temperature, the faster the decay of persistentphotoconductivity.