Research Of GaN Based MIS Structure UV Detectors

Ultraviolet （UV） detection technology has widely applied in military andcivilian field. In military field, the UV detectors can be used in missile early warning,guidance and ultraviolet communication etc., meanwhile, in civil field, they can beused in flame detection, biological-medicine analysis, ozone monitoring, sea oilmonitoring, solar illumination monitoring, public security reconnaissance and etc. Inone word, the UV detection technology is another dual-use opto-electrical detectingtechnique following the infrared and laser detecting technique.Photomultiplier tubes and similar vacuum components which are sensitive to theUV light are mostly used in high sensitive UV detection field all the time. Comparedwith the solid detectors, vacuum device has a lot of disadvantages such as largevolume, high working voltage etc; however, silicon photo-detectors （PDs）, as arepresentative of the solid detectors, are sensitive to the visible light, which willbecome a drawback in some vltraviolet applications. With more and more researchof semiconductor materials, people began to think of intrinsic ultraviolet detectorswhich have little responsivity to visible light.Gallium nitride （GaN） is a direct semiconductor with bandgap of3.4eV. ThePDs fabricated by GaN have no response to visible and infrared light, but have alarge response to the ultraviolet light with wavelength less than365nm, which isvery beneficial for detecting ultraviolet signal in the background of visible andinfrared. Besides, GaN has larger saturate electronic velocity than other III-nitrides, which means that detectors made by GaN can have more sensitivity.At present, there have been many reports about GaN based PDs. Among them,detectors of metal-semiconductor （MS） junction call for more concern because of itssimple manufacturing process, fast response, fabricating simplicity and so on. Toachieve good performance of MS UV PDs, it is important to improve crystal qualityand to achieve large Schottky barrier height at the metal-semiconductor interface. Toachieve a large Schottky barrier height on GaN, one can choose metals with highwork function. However, many of the high work function metals are not stable.Besides, severe inter-diffusion might occur at metal–GaN interface. To solve theproblem above, one can insert an insulating layer between metal and the underneathsemiconductor.In this paper, GaN based MIS structure ultraviolet detectors were fabricated byinserting a silicon nitride layer between GaN layer and metal electrode. Besides, thecharacterizations about the materials were carried out and the I-V curves and lightresponses were measured.By analyzing the current transport mechanics, it was found that thetunneling-recombination mechanism dominated at the reverse bias and with theforward bias increasing, the current transport mechanism changed from tunnelingmechanism to space charge limited current （SCLC） mechanism. The I-V curves ofthe PDs with different insulator depth showed with the insulator’ depth increasing,the current decreased.The photo responsivity measures were carried out. It is found that at5Vnegative bias, the PD fabricated by us had a relative flat response from300nm to340nm with cutoff wavelength of365nm. It had the peak responsivity of170mA/W at315nm with corresponding peak detectivity of2.3×10¹²cmHz^1/2W^-1.Interestingly, a phenomenon that with reverse bias increasing, the peak of photocurrent of the PDs redshifts was first observed，which we think can be attributed tothe tunneling procedure of the photo-generated holes assisted by defects. Besides,the light currents of PDs with different insulators were studied, and it was found the tunneling and leakage current mechanism jointly dominated the transport procedureof the light current.