Nonalloyed Ti/Al Ohmic contacts to n-type GaN using high-temperature premetallization anneal

Abstract

On Si-implanted n-type GaN, a nonalloyed Ti/Al metallization has been found to form an Ohmic contact that has a specific contact resistance as low as 1.0×10−5 Ω cm2. The Ohmic character is believed to be caused by the 1120 °C implant activation anneal which generates nitrogen vacancies that leave the surface heavily n type. This theory is indirectly confirmed on unimplanted n-type GaN by comparing the rc of nonalloyed Ti/Al on unannealed GaN with that of nonalloyed Ti/Al on 1120 °C annealed GaN. The former has rectifying electrical characteristics, while the latter forms an Ohmic contact with an rc=1.3×10−3 Ω cm2.

Contact Resistance of InGaN/GaN Light Emitting Diodes Grown on the Production Model Multi-Wafer MOVPE Reactor

“…The nitrogen vacancy in turn compensates the acceptor dopants at the metal/p-GaN interface. Several groups have already reported similar findings on these issues [7,8,9]. In addition, the presence of the high resistive Ni 3 N and Ni 4 N phases at the metal-semiconductor interface at the annealing temperature greater than 500 o C can also result in higher contact resistance [10].…”

Thermal reaction of Pt film with 〈110〉 GaN epilayer

“…This etch is a good premetallization surface treatment for GaN n-type ohmic contacts. 25 70-nm-thick Pt films were deposited on GaN by rfmagnetron sputtering with argon in a cryopumped vacuum system of 5ϫ10 Ϫ7 Torr base pressure. The samples were then annealed in a quartz vacuum-tube furnace ͑base pressure 5ϫ10 Ϫ7 Torr͒ at various temperatures between 450 and 800°C for 30 min.…”

Effect of Various Pre-Treatments on Ti/Al/Ti/Au Ohmic Contacts for AlGaN/GaN HFET Devices

“…In this case, a slight decrease in r c was observed, but the contact resistance R c did not change significantly. The improvement in r c in the case of GaN layers [3] was postulated to be due to the loss of N 2 from the annealed surface, generating N vacancies and leaving the surface heavily n-type doped. In the previous work on AlGaN/GaN HFET structures [4], pre-annealing also resulted in an increase in R s , but the decrease in r c was more significant, leading to an overall decrease in R c .…”

“…Inductively coupled plasma N 2 discharges [1], or O 2 reactive ion etching [2] have been demonstrated to reduce the contact resistance in some work. Pre-annealing, prior to metal deposition, has been also shown to reduce the contact resistance for GaN [3], and also in some cases, for AlGaN/GaN HFET structures [4], although very long pre-anneals were used in the latter case.…”