| With the remarkably development of science and technology, ultravioletdetection technology has been widely used in many fields. AlGaN based solar-blindultraviolet (SB-UV) detectors have great application prospect in early warningmonitoring, medicine, astronomy due to the advantages of being solid-state and ofsmall size, low working voltage, with good physical and chemical stability, therebysaving energy and having a long lifetime. However, the responsivity of AlGaN basedSB-UV detectors are still low compared with the traditional UV photomultiplierwhich have restrained their development and application. At present, the dislocationdensity of AlGaN material is as high as109cm–2. This problem can hardly be resolvedbefore more suitable substrates are used. It still has a lot of difficulties in improvingthe responsivity by improving the quality of the AlGaN materials. Recently, theinteraction of light with metallic nanoparticles gives rise to a diversity of profoundeffects on improving the performance of optoelectronic devices. The plasmonicphenomena offer new opportunities to engineer the performance of photodetectors viaimproved coupling between optical processes in the device active region and incidentor emitted light. In this paper, the enhancement mechanism of localized surfaceplasmons (LSPs) is also explored and discussed which has important significance tothe promote development and application of AlGaN SB-UV detectors. In this paper, the undoped AlGaN epilayer was grown on (0001) sapphiresubstrate by metal-organic chemical vapor deposition (MOCVD). SiO2mask andelectron beam evaporation method were tried to depositing Al nanoparticle arrays.Finally Al nanoparticles with controllable size are successfully made. The detectorwith MSM structure is prepared by standard photolithography process. Nickel (Ni)(50nm) Schottky contacts were fabricated for AlGaN MSM interdigitated contactsand then the samples were treated by rapid thermal annealing at450°C for180s undernitrogen atmosphere. Spectral response tests show that when the diameter of theparticle is about60nm, the strongest responsivity (288nm) increased more than2times. With the decrease of the Al particle, the peak response increased multiples alsogradually reduced. Dark current tests show that Al particles of different sizes canslightly reduce the dark current of the detector. This is mainly due to the Al2O3shellwhich passivated the screw dislocation, reducing the leakage passage. The results ofthe article research are as follows:1. The extinction spectrum of Al nanoparticles with different sizes weresimulated by finite difference time domain method. The coupling law betweenAl particles and the incident light was analyzed. A further study which theeffect of Al2O3on the redshift of extinction spectrum was carried on. At lastwe study the enhancement effect of surface plasmon resonance on detectors’performance.2. We explored the various kinds of methods for preparation of Al nanoparticles.At last we successfully mastered the preparation for Al nanoparticles withcontrollable size by electron beam evaporation.3. The AlGaN based SB-UV detector with MSM structure was prepared. Theinfluence of Al particles with different sizes on the response and dark currentof the detector are studied. It was found that the peak responsivity is thehighest for the sample with the diameter of Al NPs being60nm and theresponsivity increased from0.141A/W to0.288A/W, more than2timesenhancement. This is due to the scattering effect of the Al particles and local surface plasmon resonance caused by Al particles. Then the localized electricfield enhancement effect and related scattering effect results in moreelectron-hole pairs generated and thus a higher responsivity. The dark currentof the detectors with Al NPs is a little bit reduced compared with that withoutAl NPs. This is due to the passivation effect of the Al2O3shell which candecrease the leakage because of their terminating the screw dislocations. |
PDF Full Text Request