More Like this

1. Effect of indium accumulation on the growth and properties of ultrathin In(Ga)N/GaN quantum wells

   https://doi.org/doi.org/10.1016/j.matdes.2020.108565  

   C. Li, Y. Maidaniuk (February 2020, Crystal growth design)

   In this work, we present the investigation of InN/GaN multiple-quantum-well (MQW) growth by plasma-assisted molecular beam epitaxy using in-situ reflection high-energy electron diffraction (RHEED) to monitorthe growth process. The analysis of the RHEED intensity and pattern transitions identified an indium surface ac-cumulation even with a nominal thickness of InN as small as 0.5 monolayer (ML). This result explicitly showsthat, even at low growth temperaturesof ~550 °C, not all of the supplied indium isincorporated into the quantumwell (QW). Moreover, the residual indium can become incorporated into the GaN matrix on either side of theQW. Both QW thickness and the photoluminescence (PL) emission energy showed a self-regulating behavior.The apparent thickness did not exceed 2 MLs even when the deposited InN thickness is as large as 5 MLs. ThePL emission shows a continuous redshift with the deposited InN from ~370 nm for 0.5 ML until it saturates at~423 nm forN2 ML. Based on the observed growth phenomena, a qualitative growth model was developed to ex-plain the self-limited epitaxial growth of ultrathin In(Ga)N/GaN QWs 

   more » « less
2. Sagnac interferometry for high-sensitivity optical measurements of spin-orbit torque

   https://doi.org/10.1126/sciadv.adi9039  

   Karimeddiny, Saba; Cham, Thow Min; Smedley, Orion; Ralph, Daniel C.; Luo, Yunqiu Kelly (September 2023, Science Advances)

   Sagnac interferometry can provide a substantial improvement in signal-to-noise ratio compared to conventional magnetic imaging based on the magneto-optical Kerr effect. We show that this improvement is sufficient to allow quantitative measurements of current-induced magnetic deflections due to spin-orbit torque even in thin-film magnetic samples with perpendicular magnetic anisotropy, for which the Kerr rotation is second order in the magnetic deflection. Sagnac interferometry can also be applied beneficially for samples with in-plane anisotropy, for which the Kerr rotation is first order in the deflection angle. Optical measurements based on Sagnac interferometry can therefore provide a cross-check on electrical techniques for measuring spin-orbit torque. Different electrical techniques commonly give quantitatively inconsistent results so that Sagnac interferometry can help to identify which techniques are affected by unidentified artifacts. 

   more » « less
3. Temperature‐Dependent Properties of Atomic Layer Deposition‐Grown TiO ₂ Thin Films

   https://doi.org/10.1002/admi.202400855  

   Chowdhary, Nimarta_Kaur; Gougousi, Theodosia (January 2025, Advanced Materials Interfaces)

   Abstract This study investigates the presence of titanium oxynitride bonds in titanium dioxide (TiO₂) thin films grown by atomic layer deposition (ALD) using tetrakis dimethyl amino titanium (TDMAT) and water at temperatures between 150 and 350 °C and its effect on the films’ optical and electrical properties. Compositional analysis using X‐ray photoelectron spectroscopy (XPS) reveals increased incorporation of oxynitride bonds as the process temperature increases. Furthermore, depth profile data demonstrates an increase in the abundance of this type of bonding from the surface to the bulk of the films. Ultraviolet‐visible spectroscopy (UV‐vis) measurements correlate increased visible light absorption for the films with elevated oxynitride incorporation. The optical constants (n, k) of the films show a pronounced dependence on the process temperature that is mirrored in the film conductivity. The detection of oxynitride bonding suggests a secondary reaction pathway in this well‐established ALD process chemistry, that may impact film properties. These findings indicate that the choice of process chemistry and conditions can be used to optimize film properties for optoelectronic applications. 

   more » « less
4. Brief Paper: Quantifying Spatial Heterogeneity of Laminated Perovskite Semiconductors Using Photoluminescence Mapping

   https://doi.org/10.1115/MSEC2024-124108  

   Okia, Oluka; Lanaghan, Clare; Palmer, Jack; Yadavalli, Srinivas; Fenning, David; Dasgupta, Neil (June 2024, American Society of Mechanical Engineers)

   Abstract Halide perovskite solar cells (PSCs) are a state-of-the-art photovoltaic technology that exhibit high efficiencies and can be manufactured using roll-to-roll systems. However, PSCs are currently fabricated using sequential layer-by-layer deposition, which constrains the selection of suitable functional layers in the solar cell and limits the processing conditions and techniques that can be used. Lamination via diffusion bonding is a scalable parallel-processing technique that has the capability to overcome some of the challenges of sequential deposition by widening the thermal processing window and reducing the chemical compatibility requirements for PSC manufacturing. However, there remains a lack of detailed understanding of the process-structure-property relationships needed to accelerate the development of high-volume lamination-based manufacturing processes. In this work, we introduce a method to study the process-structure-property relationships of laminated perovskite semiconductors by using a custom photoluminescence (PL) spectroscopy system to quantify spatial heterogeneity in laminated halide perovskite (HP) materials. PL is an important figure-of-merit used to quantify the optoelectronic properties of semiconductor materials used in PV manufacturing. The spatial variation in PL of a laminated HP film is compared to that of an unlaminated HP film. The PL system uses servomotors and an Arduino microcontroller to automate a PL mapping procedure. The PL equipment is tunable to achieve a minimum possible spot size of ∼50 μm, enabling high-resolution measurements. The system is used to measure the PL of 19 separate locations on both a laminated and unlaminated HP material. The results of this study reveal that lamination at optimal conditions will improve the average PL peak intensity of the HP by 55%, indicating that lamination has the potential to improve the optoelectronic characteristics of PSCs. However, lamination also increases the standard deviation of PL peak intensity. Therefore, although lamination improves the PL of HPs, it also induces unwanted spatial heterogeneity. This warrants future studies on the governing physical mechanisms that determine quality control metrics in lamination-based PSC manufacturing. 

   more » « less
5. The Role of Ordering on the Thermoelectric Properties of Blends of Regioregular and Regiorandom Poly(3‐hexylthiophene)

   https://doi.org/10.1002/aelm.201800915  

   Lim, Eunhee; Glaudell, Anne M.; Miller, Rachel; Chabinyc, Michael L. (April 2019, Advanced Electronic Materials)

   Abstract The thermoelectric properties of semiconducting polymers are influenced by both the carrier concentration and the morphology that sets the pathways for charge transport. A combination of optical, morphological, and electrical characterization is used to assess the effect of the role of disorder on the thermoelectric properties of thin films of poly(3‐hexylthiophene) (P3HT) doped with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄TCNQ). Controlled morphologies are formed by casting blends of regioregular (RR‐P3HT) and regiorandom (RRa‐P3HT) and then subsequently doped with F₄TCNQ from the vapor phase. Optical spectroscopy and X‐ray scattering show that vapor phase doping induces order in the disordered regions of thin films and increases the long‐range connectivity of the film. The thermoelectric properties are assessed as a function of composition and it is shown that while the Seebeck coefficient is affected by structural ordering, the electrical conductivity and power factor are more strongly correlated with the long‐range connectivity of ordered domains. 

   more » « less