Cu2ZnSnS4 (CZTS) nanoparticle inks were synthesized for the first time by a one‐pot synthesis method using microwave heating. Precursor solutions were mixed and reacted at 190 °C for 30 min. Varying the initial concentration of the metal chlorides in ethylene glycol was necessary to avoid formation of copper rich and zinc poor nanoparticles. Analysis of the reaction supernatant indicates that Cu+ was fully utilized while significant amounts of Zn2+ remained unreacted. The CZTS nanoparticles were determined to be 7.6 ± 2.1 nm in diameter and were found to agglomerate into larger clusters. A solar cell fabricated with the CZTS nanoparticles had a conversion efficiency of 0.25%.

Self-assembled monolayers (SAMs) have been used to improve both the positive and negative bias-stress stability of amorphous indium gallium zinc oxide (IGZO) bottom gate thin film transistors (TFTs). N-hexylphosphonic acid (HPA) and fluorinated hexylphosphonic acid (FPA) SAMs adsorbed on IGZO back channel surfaces were shown to significantly reduce biasstress turn-on voltage shifts compared to IGZO back channel surfaces with no SAMs. FPA was found to have a lower surface energy and lower packing density than HPA, as well as lower biasstress turn-on voltage shifts. The improved stability of IGZO TFTs with SAMs can be primarily attributed to a reduction in molecular adsorption of contaminants on the IGZO back channel surface and minimal trapping states present with phosphonic acid binding to the IGZO surface. 10-15Proposed mechanisms for bias stress threshold voltage (V th ) shifts include electron trapping at the semiconductor/dielectric interface, electron injection into the dielectric, or formation of sub-band gap states in the bulk of films. It has also been suggested that adsorbed species (e.g., O 2 and H 2 O) on the back channel of the IGZO-TFTs can be the dominant mechanism for device instability, by providing acceptor or donor states or through field induced adsorption or desorption of these species. [17][18][19][20] For example, molecular oxygen can form a depletion layer at the back channel surface through electron acceptor states, while absorbed water can form an accumulation layer at the back channel surface through electron donor states.A depletion layer results in a positive V th shift, whereas an accumulation layer results in a 4 negative V th shift. Recently it has been demonstrated that dense passivation layers 21 or selfassembled monolayers (SAMs) 22 on IGZO-TFT back channels can significantly minimize these threshold voltage shifts. A potential benefit of using SAMs for surface passivation is that one can obtain well controlled chemistries at the back channel interface, even when using polymeric dielectrics for flexible electronic applications or integrating polymeric sensing layers.Herein we investigate the use of n-hexylphosphonic acid (n-HPA) and (3,3,4,4,5,5,6,6,6- IGZO-TFT test structures were fabricated using a heavily p-doped Si substrate as the gate and thermally grown SiO 2 (100 nm) as the gate dielectric. Substrates were cleaned prior to deposition of IGZO with acetone, isopropyl alcohol, and DI water. Amorphous IGZO films (~50 nm thick) were deposited using RF magnetron sputter deposition with a 3 in. IGZO target (molar composition: In 2 O 3 :Ga 2 O 3 :ZnO), 100W RF power, ~4 mTorr chamber pressure, and 20 sccm flow rate with a 1:19 (O 2 :Ar) ratio. IGZO active layers were patterned using a shadow mask 5 during deposition, and the films were subsequently annealed in air to 300 °C. Source and drain electrodes were patterned using a shadow mask during thermal evaporation of Al (~500 nm thick) giving a W/L ratio of 1000 m/100 m. Back channel surface passivation using SAMs was ...

Abstract

A method to understand the role of interfacial chemistry on the modulation of Schottky barrier heights for platinum and amorphous indium gallium zinc oxide (a-IGZO) interfaces is demonstrated through thermal processing and background ambient pressure control. In situ X-ray photoelectron spectroscopy was used to characterize the interfacial chemistries that modulate barrier heights in this system. The primary changes were a significant chemical reduction of indium, from In to In, that occurs during deposition of Pt on to the a-IGZO surface in ultrahigh vacuum. Postannealing and controlling the background ambient O pressure allows further tuning of the reduction of indium and the corresponding Schottky barrier heights from 0.17 to 0.77 eV. Understanding the detailed interfacial chemistries at Pt/a-IGZO interfaces may allow for improved electronic device performance, including Schottky diodes, memristors, and metal-semiconductor field-effect transistors.

The dehydration of hafnium oxide hydroxide sulfate thin films was studied using temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy. Films were found to desorb water up to 750 K with a maximum desorption rate at~480 K. Carbon dioxide desorption was also observed in TPD measurements, which was related to contamination of precursor solutions and/or films by CO 2 from the atmosphere. The O 1s spectra obtained for in-situ annealed samples were fit with three components corresponding to Hf-O, hydroxyl groups, and sulfate groups. Water TPD measurements from the dehydrated surface indicate the presence of two desorption states corresponding to molecularly and dissociatively adsorbed water.