Low temperature sputter-deposited ZnO films with enhanced Hall mobility using excimer laser post-processing

Abstract

We report the low temperature (T<70 ºC) fabrication of ZnO thin films (~140 nm) with Hall mobility of up to 17.3 cm 2 V-1 s-1 making them suitable for thin film transistor (TFT) applications. The films were deposited by rf magnetron sputtering at T<70 ºC and subsequently laser processed in ambient temperature in order to modify the Hall mobility and carrier concentration. Medium-to-low energy laser radiation densities and a high number of pulses were used to avoid damaging the films. Laser annealing of the films after aging in the lab under 25%-35% relative humidity and at an average illuminance of 120 lux resulted in an overall higher mobility and relatively low carrier concentration in comparison to the non-aged films that were laser processed immediately after deposition. A maximum overall measured Hall mobility of 17.3 cm 2 V-1 s-1 at a carrier density of 2.3×10 18 cm-3 was measured from a 1 GΩ as deposited and aged film after the laser treatment. We suggest that the aging of non-processed films reduces structural defects mainly at grain boundaries by air species chemisorption, with concomitant increase in thermal conductivity so that laser processing can have an enhancing effect. Such a processing combination can act synergistically and produce suitable active layers for TFT applications with low temperature processing requirements.

High‐Mobility Helical Tellurium Field‐Effect Transistors Enabled by Transfer‐Free, Low‐Temperature Direct Growth

“…This device performance is unprecedented for a semiconductor directly grown on a complementary metal oxide semiconductor (CMOS) compatible amorphous oxide at vertical integration/plastic compatible low temperatures. This Te device performance is significantly higher than other low‐temperature grown materials such as poly‐Si and ZnO, which usually exhibit mobilities below 100 cm 2 V −1 s −1 . This performance is also much higher than other synthetic vdW materials like MoS 2 on SiO 2 /Si with a mobility of ≈192 cm 2 V −1 s −1 and comparable to most of the reports of black phosphorus on SiO 2 /Si with mobilities around ≈400 cm 2 V −1 s −1 , with Te having the significant advantage of utilizing a low‐temperature, scalable growth technique, compatible with heterogeneous 3D integration and flexible devices.…”

Structural and Electronic Properties of Polycrystalline InAs Thin Films Deposited on Silicon Dioxide and Glass at Temperatures below 500 °C

“…We have shown the ability of low-temperature-grown (<500 • C) poly InAs thin films to achieve remarkable electron mobilities when measured at room temperature (~100 cm 2 /V•s), despite appearing non-uniform. The room-temperature Hall electron mobility of 155 cm 2 /V•s achieved for a heterostructure consisting of 25 nm poly GaAs + 25 nm poly InAs grown on glass (Table 1) exceeds the reported Hall mobility values of a number of other low-temperaturegrown thin-film materials, such as polycrystalline silicon [23], Hf-doped In 2 O 3 [24], ITO [25], and ZnO [26,27]. Temperature-dependent Hall effect measurements showed that surface roughness is the dominant factor limiting the electron mobility in the films, which points towards developing a planarization method for poly InAs films.…”

Excimer Laser Processing Of Igzo Thin Films For Transparent TFTs

“…These observations could be attributed to local atomic rearrangement, the amorphous structure randomness relaxation, and trap states density reduction. The local atomic rearrangement and structure relaxation caused by ELA heating, provided that no crystallisation occurs, would enhance the overlap among ns orbitals of the contained metals leading to better carrier mobility [2,11,12]. The highest observed Hall effect mobility in this work was 13.9 cm 2 /Vs obtained by ELA with single pulse at 100 mJ/cm 2 , which is very promising to apply laser treated IGZO to IGZO TFTs.…”

“…For IGZO-TFT devices, thermal and laser annealing IGZO channel layer patterns result enhanced electrical performance of IGZO TFTs. This is originated from induced changes in IGZO layers upon annealing including reduction of scattering or trapping defects density on the bulk IGZO or at its interface, enhanced atomic bonding, and amorphous structure relaxation leading to enhanced electrical prosperities of IGZO [2,11,12]. laser irradiation is also expected to reduce the contact resistance between the IGZO channel layer and the source/drain electrodes due to reduction of IGZO channels resistivity and increasing the carrier concentration upon ELA.…”