High-performance a-In-Ga-Zn-O Schottky diode with oxygen-treated metal contacts

Abstract

High-performance Schottky diodes based on palladium blocking contacts were fabricated upon depositing indium-gallium-zinc oxide (IGZO) with high oxygen content. We find that an oxygen treatment of the palladium contact is needed to achieve low off currents in the Schottky diode, and rationalize this by relating an increased oxygen content at the Pd/IGZO interface to a lower interfacial trap density. Optimized IGZO films were obtained with a record high ratio of free charge carrier density to subgap traps. The rectification ratios of diodes with such films are higher than 107 with current densities exceeding 103 A/cm2 at low forward bias of 2 V.

Flexible indium–gallium–zinc–oxide Schottky diode operating beyond 2.45 GHz

“…The cause of the barrier fluctuation is considered to be a consequence of IGZO grain boundaries, oxygen deficiency and different Pt crystalline orientations 22 . A comparison of background doping density and free carrier concentration highlights an interesting difference between IGZO and traditional covalent semiconductors, namely, not all ionized atoms in IGZO contribute free carriers; this discrepancy can be attributed to subgap traps 30 . Given the direct dependency of the C-V relationship on the background doping concentration, it is expected that the C-V barrier height shall be lower than the mean barrier height obtained by the low-temperature measurement.…”

“…At low-voltage biases, the diode performance is limited by the Schottky junction barrier instead of the IGZO mobility. The extra oxygen during the IGZO deposition is used to passivate the dangling bonds at the Schottky interface to reduce the Fermi level pinning effect 30 (shown in Supplementary Fig. 1 and Supplementary Table 1).…”

“…It is not clear why a thicker IGZO layer results in a higher Schottky barrier, perhaps it is due to the electrode evaporation process in vacuum 2,28 . Pt-IGZO Schottky barrier is sensitive to the oxygen content at the interface 30 . During the evaporation process, oxygen may escape from the IGZO layer, causing oxygen deficiency.…”

“…According to the study conducted by Olziersky et al 36 , the moderate In/Ga atom ratio of 0.95 should yield a reasonably high carrier mobility. We have therefore assumed that the mobility of IGZO is 10 cm 2 V À 1 s À 1 (roughly the mobility value obtained from TFTs based on similar IGZO material 22,28,30 ). Figure 1d shows that the barrier height can be obtained from the sum of V bi and E C À E F .…”

“…Metal-oxide semiconductors, on the other hand, have already been incorporated into flexible electronics in both academia and industry 7,8,21,22 . To date, most research on metaloxide semiconductors has focused on thin-film transistors (TFTs) 7,8,[21][22][23] , and little has been reported on diodes [24][25][26][27][28][29][30] 27), but these were all made on glass substrate using high-temperature annealing processes and hence not applicable to flexible substrates. To the best of our knowledge, the highest frequency obtained on plastic substrates was 27 MHz by IGZOCu 2 O diodes 10 .…”