Sputter Deposition of Transition Metal Oxides on Silicon: Evidencing the Role of Oxygen Bombardment for Fermi‐Level Pinning

Abstract

Different magnetron sputtering‐based deposition methods of nickel oxide SiO2‐passivated Si surfaces are compared. Results highlight that the presence of oxygen in the deposition chamber during reactive sputtering drastically affects the Si/SiO2 interface. An alternative method for the preparation of NiO is the sputtering of metallic nickel in oxygen‐free atmosphere followed by a post oxidation of the deposited layer in an oxygen atmosphere without plasma exposition is proposed. This method is introduced as metal layer oxidation (MLO). Using this technique, the barrier height on n‐type silicon increases from ≈0.4 eV for reactively sputtered NiO to more than 0.6 eV for the MLO method. In situ photoelectron spectroscopy evidences the formation of an extra electronic state when NiO is reactively sputtered, which is assigned to the intense oxygen ion bombardment of the Si/SiO2 surface during the process. This extra‐electronic state pins the silicon energy bands in an undesirable position. The extra‐electronic state is associated with oxygen interstitial in the SiO2 implanted during reactive sputtering.

Electronic and Chemical Properties of Nickel Oxide Thin Films and the Intrinsic Defects Compensation Mechanism

“…The defect concentration must be at least >1% as they are detected both by PES and EELS measurements. For such concentration, the width of the depletion layer at the grain boundaries must be in the nanometers range for a defect-free bulk. − It can be, however, assumed that ionic oxygen bombardment under reactive sputtering induces defects that are immobilized at room temperature in the thin films structure, even when sputtered at low oxygen concentration. Therefore, bulk defects cannot be excluded at room temperature although not detected by EELS.…”

“…Nickel oxide (NiO) is a versatile prototypal charge transfer p-type transition metal oxide material, having a wide optical band gap (∼3.6–4.3 eV) and crystallizing in a cubic rock-salt-like structure. , An abundant literature describing NiO properties is available because of its potential for being implemented in a wide set of applications, e.g., organic/inorganic electronic devices, − volatile memory, , gas sensor, catalysis, − and energy storage. ,− …”

How flat is the flatband potential?

“…For this reason, the temperature and the pressure during the Pt deposition are not indicated in the article. The nickel oxide (NiO) layer is deposited by Metal Layer Oxidation (MLO), which consists in separating the stage of deposition to the stage of oxidation for avoiding the formation of oxygen interstitial in the Si/SiO 2 interface 40 during sputtering. MLO is prepared from a nickel metallic target at 1 Pa in an oxygen free atmosphere and is followed by an oxidation step in the presence of oxygen at 1–6 Pa either at room temperature (RT) or higher temperature (HT) when prepared between 100 °C and 200 °C.…”

“…As detailed in a previous article, PES measurements show that the NiO layer prepared by MLO is conform to standard NiO layers. 40…”

Avoiding Fermi Level Pinning at the SnS Interface for High Open-Circuit Voltage

“…Intrinsic surface states and induced gap states, which can pin the Fermi energy, are absent at the interfaces between two semiconductors; therefore, these cannot be responsible for the limited Fermi-level shifts at such interfaces of SnS. (ii) Crystallographic defects at interfaces (point defects, dislocations) can also induce Fermi-level pinning at interfaces, which is caused by chemical reactions during interface formation or by lattice mismatch . Such defects are not intrinsic to the interface and can potentially be avoided through selecting suitable contact materials and contact processing.…”