The Research And Fabrication Of GaN-based Materials And MSM UV-Photodetectors

GaN has d1rect, wide bandgap und is one of the II1ost promisinglnateria1. 1t's good e1ectrica1, opt ica1 characteristi cs and excel1entlllecllaniczl1 properties make it one of the most ideal choices for short wavephotoe1ectron devices, such as u1 travio1et photodetectors. I,otent ia1uses of such (UV) photodetectors inc1ude scientific research, mi 1 itary,space--based, envirommental and soIl1e industria1 aDI)l icat i ons. 1'helneta1--semi conductor--metal (MSM) structure is an at tract i ve carld idate f()r;i UV Photodetector because of its p1ane structure, fabri cat ion simp1 i ci ty,the easifless of integrat ion. So, GaN--based MSM UV photodetector has beenone of the focuses of iflterest in recent years. In this paper, accordiflgto the working pri nci p1es of devi cG, we design the struc ture narameter ofdevice, and then the hexagona1 and cubic GaN epitaxial layers were grown.on sapp1re and GaAs substrates respect ive1y. As a resu1 t, We havefabricated GaN--based MSM UV photodetectors, the responsi vity of devicereach 0. 21A/W, and a1so get some other significative resul t.Mair1 works and resu1t inc1ude:(l) By ana1yzing the the working pril1ci p1es of GaN--based MSM ph()to-detectors, we designed the two ki11ds of di fferent structure parameterof device. The electrode fingers are 2 p m wide, and l00 ll nl long, the gap..sI)iicing 1s 6 ll nl. l0 ll m respecti vc1y. The effective area of device isl()4 ll mX 155 ll m. 150 ll mX 155 ll m respective1y.(2) IIexagofla1 and cubic GaN epitaxia1 1ayers were grown by meta1organicchemical vapoI' deposit ion (M0CVD). The X--ray di ffract ion (XRD), photo-1umi nescence (I3L), Raman scatter i ng spectra (Raman ) were appl ied tos tudy the samp1es, and we made some detai 1ed discuss ion. According toXl{D result, we got the 1attico constant of the three saInples (twosamples are hexagona1: 1#. 2#, one is cubi c: 3#) are 0. 5l22nm. 0. 5214nm.(). 4469nm respect ive1 y. The l7I. peak of 1#. 2# samp1 es a1'e narrow, their3gn ghFWIlM are only 7. 5nm and 10nm respec Live1y, but the ye1 l ()w band i s alsofound on the IJL spectra of these two samp1es. The yel low peak i s verystrong in 1# samp1e, its intensi ty is higher than that of the Ilear--bandpeak. While the ye11ow band is quite weak compairing with the 1#samp1e, and its radio of ye1low --band/ near--band is on1y 0. 17. The PLsignal peak is near1y absent at room temperature, we found its signalpeak on1y at very 1ow temperature. Combining the resu1t of l{alnanspectra, we reach the conclusion that the crysta1 qua1 i ty of 2# sall1p1eis better than that of 1# sample, afld 3# samp1e is the worst.(3) The mask p1ate of the optical 1 ithography were protracted usir1g Ledit7. 50. We fabricated the GaN--based MSM photodetectors successful1 yusing the 1 if t--off technics(4) The spectrum respone, dark current, current--voltage UI1deri 11uminatiofl of our GaN--based MSM photodetectors were measured andstud ied. Both device (l#. 2# ) got good responsi tivi ty at bafld edge,and show a very abrupt cutoff for wave1e11gth 1onger than gaf), whichind icate a good visble bl ifldness. llut the dark curre[lt ot devices arere1ative high, the value is 52 ll A. 27 p A respective1y at 12V bias. 1'heresponsitivity reach 0. 18 A/W and 0. 21A/W, which is rather good indomestic. And the breakdown vo1tage of both detectors (l#. 2#) is veryhigh, we found appearance of breakdown ofl1y when the bias reacb 250V.As for our 3# detector, we didn' t find response, which may attributeto the difficulty in cubic GaN growth and the bad qua1ity of theepitaxia1 1ayer. To date, we don' t find any report about the cubicGaN--based MSM photodetectors.