Direct Nanoscale Characterization of Deep Levels in AgCuInGaSe2 Using Electron Energy‐Loss Spectroscopy in the Scanning Transmission Electron Microscope. Issue 35 (5th August 2019)

• Record Type: Journal Article
• Authors: Deitz, Julia I.; Paul, Pran K.; Farshchi, Rouin; Poplavskyy, Dmitry; Bailey, Jeff; Arehart, Aaron R.; McComb, David W.; Grassman, Tyler J.
• Is Part Of: Advanced energy materials. Volume 9:Issue 35(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-08-05
• Subjects: defect characterization -- electron energy‐loss spectroscopy -- electron microscopy -- photovoltaics -- semiconductors; Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.201901612
• Languages: English
• ISSNs: 1614-6832

Abstract

Abstract: A new experimental framework for the characterization of defects in semiconductors is demonstrated. Through the direct, energy‐resolved correlation of three analytical techniques spanning six orders of magnitude in spatial resolution, a critical mid‐bandgap electronic trap level ( E V + 0.56 eV) within Ag0.2 Cu0.8 In1− x Ga x Se2 is traced to its nanoscale physical location and chemical source. This is achieved through a stepwise, site‐specific correlated characterization workflow consisting of device‐scale (≈1 mm 2 ) deep level transient spectroscopy (DLTS) to survey the traps present, scanning probe–based DLTS (scanning‐DLTS) for mesoscale‐resolved (hundreds of nanometers) mapping of the target trap state's spatial distribution, and scanning transmission electron microscope based electron energy‐loss spectroscopy (STEM‐EELS) and X‐ray energy‐dispersive spectroscopy for nanoscale energy‐, structure, and chemical‐resolved investigation of the defect source. This first demonstration of the direct observation of sub‐bandgap defect levels via STEM‐EELS, combined with the DLTS methods, provides strong evidence that the long‐suspected CuIn/Ga substitutional defects are indeed the most likely source of the E V + 0.56 eV trap state and serves as a key example of this approach for the fundamental identification of defects within semiconductors, in general. Abstract : Nanoscale defect structures can have an outsized impact on macroscale semiconductor material properties and device behavior, but definitively understanding the underlying causes and effects can be exceedingly difficult. A novel multiscale, correlative characterization framework that enables the direct discovery of these important structure–property links is introduced and used to identify a key, ubiquitous defect in the AgCuInGaSe2 thin‐film photovoltaic system.