Amorphous ZnOxNy thin films with high electron Hall mobility exceeding 200 cm2 V−1 s−1

Abstract

Zinc oxynitride (ZnOxNy) has attracted much attention as an amorphous semiconductor with high electron mobility. Recent studies reported that ZnOxNy thin films grown by sputtering contained nanocrystals, which might reduce their electron mobility through grain boundary scattering. In this study, we fabricated amorphous ZnOxNy thin films on a glass substrate by a less-energetic nitrogen-plasma-assisted pulsed laser deposition (PLD) to suppress the formation of the nanocrystals. Grown by PLD under optimized conditions, these ZnOxNy thin films exhibited extremely flat surfaces with a root-mean-squared roughness (Rrms) of less than 0.3 nm. The Hall mobility of these films exceeded 200 cm2 V−1 s−1 at a critical carrier concentration of ∼1 × 1019 cm−3, which was twice as high as the reported values for sputter-deposited films. Meanwhile, the mobility of films with larger Rrms was limited to ∼160 cm2 V−1 s−1 even at the critical carrier concentration and comparable with that of the sputter-deposited ZnOxNy films. The substantial enhancement in mobility in extremely flat ZnOxNy films demonstrated that suppressing the formation of nanocrystals is the key to fabricating amorphous ZnOxNy thin films with very high mobility.

Electronic structure and transport in amorphous metal oxide and amorphous metal oxynitride semiconductors

“…Also, owing to the large number of such pairs with higher orbital overlap, the total normalized or- bital overlap integral for a-ZnON is much higher (more than a factor of 2) compared to a-IGZO and hence, we may expect the electron transport to be much easier in a-ZnON. From literature [16][17][18][19][20]31,36 , we know that the measured Hall mobilities for a-ZnON are much higher compared to a-IGZO, which is consistent with higher values of normalized orbital overlap integrals, observed from our calculations, for a-ZnON compared to a-IGZO.…”

Electronic Defects in Amorphous Oxide Semiconductors: A Review

“…In addition, higher mobilities >30 cm 2 V −1 s −1 are available for In‐rich AOSs and other AOSs such as a‐In‐Sn‐Zn‐O (ITZO) and a‐In‐Al‐Zn‐O (IAZO) TFTs (note that the constituent elements in the IAZO are not described in the paper but presented at the corresponding SID2014 conference). Very high μ FE ≈100 cm 2 V −1 s −1 have been reported for amorphous Zn‐O‐N TFTs (note that up to 240 cm 2 V −1 s −1 of Hall mobility was also reported).…”

Physical properties of reactive RF sputtered a-IZON thin films.

“…All deposited films were amorphous, independently of the sputtering power used in the deposition, and the related spectra showed a broad band (bump) in the diffracted intensity associated with the amorphous phase in the range of 30 • -35 • with the maximum approximately 32.4 • . This band is related to the amorphous IZO matrix, so it is not possible to observe evident effect of nitrogen for these cases however, it is well known that typically the IZO thin films tend to crystallize and the XRD pattern shows an intense, sharp peak at 2θ=33.2 • related with the orientation (222) of pure In 2 O 3 [10][11][12], but in this case the IZON films showed a marked suppression of the typical crystallization of IZO, inclusive for the film deposited at 120 W.…”

“…For example, monometallic and bimetallic oxynitrides have been investigated as catalysts [1], lithium phosphorus oxynitrides have been applied in thin film lithium ion batteries [2], titanium oxynitride has been developed for optical hard coatings [3], titanium niobium oxynitride has been applied in photocatalysis [4], indium and indium tin oxynitrides have been used for specific applications like gas sensors and high temperature thin film thermocouples [5,6], aluminum oxynitride has been applied as transparent and conductive layers in optoelectronic devices [7], and zinc oxynitrides have been conceded as a strong substitute to conventional semiconductor film such as silicon due to high mobility value [8,9]. In this context, as general rule, amorphous oxynitrides have much higher charge carrier mobility than a-Si [10][11][12]. At the same time, amorphous oxynitrides presents homogeneous uniformity and high structural stability even though simple binary oxides tend to crystallize [13,14].…”