Search

Recent discoveries reveal that extracellular vesicles (EVs) play an important role in transmitting signals. Although this emerging transcellular pathway enables a better understanding of neural communication, the lack of techniques for effectively isolating EVs impedes their studies. Herein, we report an emergent high-throughput platform consisting of three-dimensional carbon nanotube arrays that rapidly capture different EVs based on their sizes, without any labels. More importantly, this label-free capture maintains the integrity of the EVs when they are excreted from a host cell, thus allowing comprehensive downstream analyses using conventional approaches. To study neural communication, we developed a stamping technique to construct a gradient of nanotube herringbone arrays and integrated them into a microdevice that allowed us processing of a wide range of sample volumes, microliters to milliliters, in several minutes through a syringe via manual hand pushing and without any sample preparation. This microdevice successfully captured and separated EVs excreted from glial cells into subgroups according to their sizes. During capture, this technology preserved the structural integrity and originality of the EVs that enabled us to monitor and follow internalization of EVs of different sizes by neurons and cells. As a proof of concept, our results showed that smaller EVs (∼80 nm in diameter) have a higher uptake efficiency compared to larger EVs (∼300 nm in diameter). In addition, after being internalized, small EVs could enter endoplasmic reticulum and Golgi but not the largest ones. Our platform significantly shortens sample preparation, allows the profiling of the different EVs based on their size, and facilitates the understanding of extracellular communication. Thus, it leads to early diagnostics and the development of novel therapeutics for neurological diseases.

Hexagonal boron nitride (hBN) has received much attention in recent years as a 2D dielectric material with potential applications ranging from catalysts to electronics. hBN is a stable covalent compound with a planar hexagonal lattice and is relatively unreactive to most chemical environments, making the chemical functionalization of hBN challenging. Here, a simple, scalable strategy to fluorinate hBN using a direct gas-phase fluorination technique is reported. The nature of fluorine bonding to the hBN lattice and their chemical coordination are described based on various characterization studies and theoretical models. The fluorine functionalized hBN shows a bandgap reduction and displays a semiconducting behavior due to the fluorination process. Additionally, the fluorinated hBN shows significant improvement in its thermal and friction properties, which could be substantial in applications such as lubricants and thermal fluids. Theory and simulations reveal that the enhanced friction properties of fluorinated hBN result from reduced inter-planar interaction energy by electrostatic repulsion of intercalated fluorine atoms between hBN layers without significant disruption of the in-plane lattice. This technique paves the way for the fluorination of several other 2D structures for various applications such as magnetism and functional nanoscale electronic devices.

Piezoelectricity in low-dimensional materials and metal-semiconductor junctions has attracted recent attention. Herein, a 2D in-plane metal-semiconductor junction made of multilayer 2H and 1T' phases of molybdenum(IV) telluride (MoTe

A brief overview of quantum materials and their prospects for applications, in the near, mid, and far-term in the areas of quantum information science, spintronics, valleytronics, and twistronics and those involving topology are covered in this perspective. The material and processing challenges that will modulate the realism of the applications will be discussed as well.

Two-dimensional semiconductors, in particular transition metal dichalcogenides and related heterostructures, have gained increasing interest as they constitute potential new building blocks for the next generation of electronic and optoelectronic applications. In this work, we develop a novel nondestructive and noncontact technique for mapping the absorption properties of 2D materials, by taking advantage of the underlying substrate cathodoluminescence emission. We map the quantitative absorption of MoS2 and MoSe2 monolayers, obtained on sapphire and oxidized silicon, with nanoscale resolution. We extend our technique to the characterization of the absorption properties of MoS2/MoSe2 van der Waals heterostructures. We demonstrate that interlayer excitonic phenomena enhance the absorption in the UV range. Our technique also highlights the presence of defects such as grain boundaries and ad-layers. We provide measurements on the absorption of grain boundaries in monolayer MoS2 at different merging angles. We observe a higher absorption yield of randomly oriented monolayers with respect to 60° rotated monolayers. This work opens up a new possibility for characterizing the functional properties two dimensional semiconductors at the nanoscale.

The reach and the rate of spread of viral infectious diseases have vastly increased owing to changes in various environmental, biological, socioeconomic, and political factors as well as expansion of international travel and trade. Consequently, the need for more rapid outbreak detection and efficient monitoring of the spread of the infection to minimize the burden on global health and the economy has also become of paramount importance. Rapid isolation, identification, and full characterization of viruses from field samples are critical in the prevention of the epidemics. In this regard, nanotechnology has emerged as a significant platform for human health care and point-of-care diagnosis of interactions in the cellular and subcellular scales. This chapter presents a review of the exploration of low-dimensional materials, such as carbon nanotubes and transition metal dichalcogenides in developing lab-on-a-chip system applicable in virology as a point-of-care device for size-based virus capture and enrichment for any virus. Future prospects of these materials in epidemiology are also discussed.

Multi-layer, metallo-dielectric structures (screens) have long been employed as electromagnetic band filters, either in transmission or in reflection modes. Here we study the radiation energy not transmitted or reflected by these structures (trapped radiation, which is denoted—absorption). The trapped radiation leads to hot surfaces. In these bi-layer screens, the top (front) screen is made of metallic hole-array and the bottom (back) screen is made of metallic disk-array. The gap between them is filled with an array of dielectric spheres. The spheres are embedded in a dielectric host material, which is made of either a heat-insulating (air, polyimide) or heat-conducting (MgO) layer. Electromagnetic intensity trapping of 97% is obtained when a 0.15 micron gap is filled with MgO and Si spheres, which are treated as pure dielectrics (namely, with no added absorption loss). Envisioned applications are anti-fogging surfaces, electromagnetic shields, and energy harvesting structures.

Optical spectroscopy (OS) techniques are often coupled with first-principles density functional theoretical (DFT) calculations for determining the precise influence of defects on the electronic and structural properties of two-dimensional (2D) transition metal dichalcogenides. Such calculations are carried out presuming there is little or no effect of vibrational transitions on the observed electronic spectrum. However, if the effect of change in vibrational energy (Franck Condon (FC) shift) associated with such a transition is large, it could possibly lead to a different origin for the observed peak. One such instance is the attribution of the 0.75 eV cathodoluminescence peak by Fabbri et al (2016 Nat. Commun. 7 13044) to an optical transition from an S vacancy level in the band gap, under the assumption that the FC shift is negligible. Here, by first principles constrained DFT calculations using hybrid HSE06 functional we show that this combined prediction of OS and DFT calculations is valid for 2D MoS

The structural defects in two-dimensional transition metal dichalcogenides, including point defects, dislocations and grain boundaries, are scarcely considered regarding their potential to manipulate the electrical and optical properties of this class of materials, notwithstanding the significant advances already made. Indeed, impurities and vacancies may influence the exciton population, create disorder-induced localization, as well as modify the electrical behaviour of the material. Here we report on the experimental evidence, confirmed by ab initio calculations, that sulfur vacancies give rise to a novel near-infrared emission peak around 0.75 eV in exfoliated MoS2 flakes. In addition, we demonstrate an excess of sulfur vacancies at the flake's edges by means of cathodoluminescence mapping, aberration-corrected transmission electron microscopy imaging and electron energy loss analyses. Moreover, we show that ripplocations, extended line defects peculiar to this material, broaden and redshift the MoS2 indirect bandgap emission., Impurities and vacancies are commonly found within the crystalline lattice of transition metal dichalcogenides, however they are usually seen as detrimental for their optical properties. Here, the authors demonstrate that sulfur vacancies in MoS2 can give rise to a near-infrared emission peak.

We present experimental demonstration utilizing phase-shifting resonant vibrometry to determine the presence and position of embedded defect inside a device under test (DUT) whose awkward surface shape prohibits the use of conventional ultrasonic transducers.

In the realm of layered materials beyond graphene, MoS2 gains a primary role due to its semiconducting nature and n-type transport down to the 2D limit that makes it extremely appealing for electronic and optoelectronic applications. The intrinsic presence of defects causes MoS2 to undergo localization effects. In the present work, solid evidence of Cs impurities in bulky MoS2 crystals in a concentration well beyond the sensitivity threshold of independent compositional spectrometry probes is brought. Unlike conventional intercalation of alkali metals in MoS2, on the basis of the measured crystal structure and ab initio calculations, it is proposed that the incorporation of Cs is stabilized by complex where one Cs atom is associated with a double S vacancy therein resulting in an overall n-type doping of the MoS2. The field effect transistor based on this kind of Cs-doped MoS2 multilayer flakes exhibits a variable range hopping transport and a metal-insulator transition.

The papers in this special issue explore Device Concepts, Architectural Strategies, and Interfacing Methodologies for Realizing Nanoscale Sensor Systems. This is volume II of the special issue. Some of the papers are based in part on oral and poster presentations at the Nanoelectronic Devices for Defense and Security Conference, held in Fort Lauderdale, FL, from September 27-October 2, 2009.

The twenty papers in this special issue explore device concepts, architectural strategies and interfacing methodologies for nanoscale sensor systems. Some of the papers are based in part on oral and poster presentations at the Nanoelectronic Devices for Defense and Security Conference, held in Fort Lauderdale, FL, from September 27-October 2, 2009.

Topological insulators have been the subject of intense research interest due to their unique surface states that are topologically protected against scattering or defects. However, the relationship between the crystal structure and topological insulator state remains to be clarified. Here, we show the effects of hydrostatic pressure on the structural, vibrational, and topological properties of the topological insulator Bi1.5Sb0.5Te1.8Se1.2 up to 45 GPa using X-ray diffraction and Raman spectroscopy in a diamond anvil cell, together with first-principles theoretical calculations. Two pressure-induced structural phase transitions were observed: from ambient rhombohedral R 3¯m phase to a monoclinic C2/m phase at ∼13 GPa, and to a disordered I4/mmm phase at ∼22 GPa. In addition, the alloy undergoes several electronic transitions within the R 3¯m phase: indirect to direct bulk band gap transition at ∼5.8 GPa, bulk gap closing with an appearance of Dirac semimetal (DSM) state at ∼8.2 GPa, and to a trivial semimetal state at ∼12.1 GPa. Anomalies in c/a ratio and Raman full width at half maximum that coincide with the DSM phase suggest the contribution of electron-phonon coupling to the transition. Compared to binary end members Bi2Te3, Bi2Se3, and Sb2Te3, the structural phase transition and anomaly were observed at higher pressures in Bi1.5Sb0.5Te1.8Se1.2. These results suggest that the topological transitions are precursors to the structural phase transitions.

Optical spectroscopy (OS) techniques are often coupled with first-principles density functional theoretical (DFT) calculations for determining the precise influence of defects on the electronic and structural properties of two-dimensional (2D) transition metal dichalcogenides. Such calculations are carried out presuming there is little or no effect of vibrational transitions on the observed electronic spectrum. However, if the effect of change in vibrational energy (Franck Condon (FC) shift) associated with such a transition is large, it could possibly lead to a different origin for the observed peak. One such instance is the attribution of the 0.75 eV cathodoluminescence peak by Fabbri et al (2016 Nat. Commun. 7 13044) to an optical transition from an S vacancy level in the band gap, under the assumption that the FC shift is negligible. Here, by first principles constrained DFT calculations using hybrid HSE06 functional we show that this combined prediction of OS and DFT calculations is valid for 2D MoS2 since the FC shift associated with electronic transitions from a sulfur vacancy is indeed small ~28 meV. Based on our calculations we conclude that it is reasonable to make a direct connection between DFT calculations and optical spectroscopy techniques in this material, hence, establishing a one to one relation between defect related emission bands and electronic transitions from the defect levels.

Previously, we demonstrated a large format 1024 × 1024 corrugated quantum well infrared photodetector focal plane array (C-QWIP FPA). The FPA has a cutoff at 8.6 μm and is BLIP at 76 K with f /1.8 optics. The pixel had a shallow trapezoidal geometry that simplified processing but limited the quantum efficiency QE. In this paper, we will present two approaches to achieve a larger QE for the C-QWIPs. The first approach increases the size of the corrugations for more active volume and adopts a nearly triangular pixel geometry for larger light reflecting surfaces. With these improvements, QE is predicted to be about 35% for a pair of inclined sidewalls, which is more than twice the previous value. The second approach is to use Fabry–Perot resonant oscillations inside the corrugated cavities to enhance the vertical electric field strength. With this approach, a larger QE of 50% can be achieved within certain spectral regions without using either very thick active layers or anti-reflection coatings. The former approach has been adopted to produce two FPAs, and the preliminary experimental results will be discussed. In this paper, we also describe using voltage tunable detector materials to achieve multi-color capability for these FPAs.

A method for formulating the unit cell of arbitrarily stacked, two-dimensional (2D) transition metal dichalcogenides is presented. Geometrical considerations and genetic algorithms are used to minimize the number of unit cells utilized in the construction of a supercell which may accommodate the lattice constants of arbitrary 2D and other close-packed materials. Supercells for various combinations of layered 2D transition metal dichalcogenides are calculated and their electronic band structures are simulated using density functional theory. Results are compared with previously reported density functional theory simulations from the literature.

A method of synthesizing monolayers of molybdenum disulfide (MoS2) via chemical vapor deposition is described. In this process a tube furnace is used to evaporate MoS2 over silicon/silicon dioxide substrates. Sulfur is then evaporated and flown over the substrates via a stream of inert gas. Optical and scanning electron microscopy and Raman spectroscopy are utilized to characterize the growth of the MoS2 monolayers. Density-functional theory simulations are used to compare theoretical predictions to the observed photoluminescence

Here, we present detailed results of Raman and photoluminescence (PL) characterization of monolayers of MoS2 grown by chemical vapor deposition (CVD) on SiO2/Si substrates after thermal annealing at 150 °C, 200 °C, and 250 °C in an argon atmosphere. In comparison to the as-grown monolayers, annealing in the temperature range of 150–250 °C brings about significant changes in the band edge luminescence. It is observed that annealing at 150 °C gives rise to a 100-fold increase in the PL intensity and produces a strong band at 1.852 eV attributed to a free-to-bound transition that dominates over the band edge excitonic luminescence. This band disappears for the higher annealing temperatures. The improvement in PL after the 200 °C anneal is reduced in comparison to that obtained after the 150 °C anneal; this is suggested to arise from a decrease in the non-radiative lifetime caused by the creation of sulfur di-vacancies. Annealing at 250 °C degrades the PL in comparison to the as-grown sample because of the on...

We have studied the influence of an external electric field on the band structures of graphene fluoride in C 4 F stoichiometry using Density Functional Theory (DFT). The electric field was applied in two different directions, field pointing towards the fluorine layer and in opposite direction pointing towards the graphene layer, normal to the plane of the bilayers. Calculations reveal that the band gaps are tunable with electric field and are modulated based on the direction of the field. The gap increases by 35 meV in one direction and decreases by 35 meV in the opposite direction at a maximum applied field of 3.3 V/nm.

The development and demonstration of a new snapshot hyperspectral sensor is described. The system is a significant extension of the four dimensional imaging spectrometer (4DIS) concept, which resolves all four dimensions of hyperspectral imaging data (2D spatial, spectral, and temporal) in real-time. The new sensor, dubbed "4×4DIS" uses a single fiber optic reformatter that feeds into four separate, miniature visible to near-infrared (VNIR) imaging spectrometers, providing significantly better spatial resolution than previous systems. Full data cubes are captured in each frame period without scanning, i.e., "HyperVideo". The current system operates up to 30 Hz (i.e., 30 cubes/s), has 300 spectral bands from 400 to 1100 nm (~2.4 nm resolution), and a spatial resolution of 44×40 pixels. An additional 1.4 Megapixel video camera provides scene context and effectively sharpens the spatial resolution of the hyperspectral data. Essentially, the 4×4DIS provides a 2D spatially resolved grid of 44×40 = 1760 separate spectral measurements every 33 ms, which is overlaid on the detailed spatial information provided by the context camera. The system can use a wide range of off-the-shelf lenses and can either be operated so that the fields of view match, or in a "spectral fovea" mode, in which the 4×4DIS system uses narrow field of view optics, and is cued by a wider field of view context camera. Unlike other hyperspectral snapshot schemes, which require intensive computations to deconvolve the data (e.g., Computed Tomographic Imaging Spectrometer), the 4×4DIS requires only a linear remapping, enabling real-time display and analysis. The system concept has a range of applications including biomedical imaging, missile defense, infrared counter measure (IRCM) threat characterization, and ground based remote sensing.

We demonstrate the use of a high sensitivity pulsed laser vibrometer to determine remotely the detailed, time-phased mechanical workings of various parts of the human heart. Results reported are validated by electrocardiography and accelerometer readings.

Trustworthy location information is important because it is a critical input to a wide variety of location-based applications. However, the localization infrastructure is vulnerable to physical attacks and consequently the localization results are affected. In this paper, we focus on achieving robust wireless localization when attacks are present on access points. We first investigate the effects of attacks on localization. We then derive an attack-resistant scheme that can be integrated with existing localization algorithms and are not algorithm-specific. Our attack-resistant scheme are based on K-means clustering analysis. We examined our approach using received signal strength (RSS) in widely used lateration-based algorithms. We validated our method in the ORBIT testbed with an IEEE 802.11 (Wi-Fi) network. Our experimental results demonstrate that our proposed approach can achieve comparable localization performance when under access-point attacks as compared to normal situations without attack.

In this paper we discuss a random walk model to characterize the pulse discharge battery process. Several theoretical results are derived including the mean and variance of an unattended battery-driven sensor lifetime. Some numerical results are presented.

Measurements of differential cross sections (DCSs) for electron-impact excitation of the ${a}^{\ensuremath{''}}\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}_{g}^{+}$, $b\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Pi}_{u}$, ${c}_{3}\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Pi}_{u}$, ${o}_{3}\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Pi}_{u}$, ${b}^{\ensuremath{'}}\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}_{u}^{+}$, ${c}_{4}^{\ensuremath{'}}\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}_{u}^{+}$, $G\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}_{u}$, and $F\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}_{u}$ states in ${\mathrm{N}}_{2}$ from the $X\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}_{g}^{+}({v}^{\ensuremath{''}}=0)$ ground level are presented. The DCSs were obtained from energy-loss spectra in the region of $12\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}13.82\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ measured at incident energies of 17.5, 20, 30, 50, and $100\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and for scattering angles ranging from 2\ifmmode^\circ\else\textdegree\fi{} to 130\ifmmode^\circ\else\textdegree\fi{}. The analysis of the spectra follows a different algorithm from that employed in a previous study of ${\mathrm{N}}_{2}$ for the valence states [Khakoo et al. Phys. Rev. A 71, 062703 (2005)], since the $\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Pi}_{u}$ and $\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}_{u}^{+}$ states form strongly interacting Rydberg-valence series. The results are compared with existing data.

Under relatively high pump intensities, photoluminescence intensities across the miniband were greatly reduced, which was attributed to the existence of periodic electric fields caused by spatially-separated photogenerated electrons and holes in short-period type-II InAs/GaSb superlattices.

Current generation QWIP detectors, although very cost effective, have relatively narrow spectral range and low quantum efficiencies. Tactical operation is generally limited to a single spectral band. These limitations arise from the design approach and restrict applications to those that can tolerate these performance limitations. Using recent device design improvements, a novel material, and special processing approaches, High Quantum Efficiency Dual Band C-QWIP detectors are currently being developed. These are expected to overcome traditional limitations in the QWIP design approach and deliver extremely high performance. In the first phase of the program, single color LWIR and VLWIR C-QWIP FPAs in large (1024x1024) format will be demonstrated with targeted peak quantum efficiency of 35%, and correspondingly high BLIP operating temperatures. In the next phase of the program, the team will continue to improve QE towards 50% with conversion efficiency of 75%, and demonstrate dual band MW/LW FPAs. The detector gain will be optimized for operation in either low background or high background applications. These goals will be accomplished using highly producible/low cost materials and processes. System considerations include ROIC well capacity, noise performance, as optics configuration and other concerns will be addressed. A robust design for high performance in a variety of applications will be shown. This work is being performed by the Army Research Laboratory (ARL) and L-3 Cincinnati Electronics (CE), with funding provided by the Missile Defense Agency.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Previously, we demonstrated a large format 1024 x 1024 corrugated quantum well infrared photodetector focal plane array (C-QWIP FPA). The FPA has a cutoff at 8.6 μm and is BLIP at 76 K with f/1.8 optics. The pixel had a shallow trapezoidal geometry that simplified processing but limited the quantum efficiency QE. In this paper, we will present two approaches to achieve a larger QE for the C-QWIPs. The first approach increases the size of the corrugations for more active volume and adopts a nearly triangular pixel geometry for larger light reflecting surfaces. With these improvements, QE is predicted to be about 35% for a pair of inclined sidewalls, which is more than twice the previous value. The second approach is to use Fabry-Perot resonant oscillations inside the corrugated cavities to enhance the vertical electric field strength. With this approach, a larger QE of 50% can be achieved within certain spectral regions without using either very thick active layers or anti-reflection coatings. The former approach has been adopted to produce a series single color FPAs, and the experimental results will be discussed in a companion paper. In this paper, we also describe using voltage tunable detector materials to achieve multi-color capability for these FPAs.

The Type II broken band-gap alignment in semiconductor structures wherein the conduction band minimum is in one semiconductor (e.g., InAs) and the valence band maximum is in another (e.g., GaInSb) offers certain unique advantages which can be utilized to realize band-gap engineered novel quantum electro-optic devices such as lasers and detectors. The advantages of the type II structures include reduced Auger recombination, extending the effective band-gap energy of materials wherein type I band-gap alignment would give rise to difficulties such as miscibility gap. In this paper we describe the work carried out at the Army Research Laboratory on type II semiconductor quantum electro-optic devices such as IR lasers and detectors operating in the 3-12 μm range. Specifically we will cover the progress made in GaSb based type II strained layer superlattice IR detectors and Interband Cascade IR Lasers. We will also present our recent work in self-assembled quantum dots which have type II band-gap alignment with the matrix material in which the dots are embedded.

We present first-principles calculations on the bandgap of graphene on a layer of hexagonal boron nitride in three different stacking configurations. Relative stability of the configurations is identified and bandgap tunability is demonstrated through the application of an external, perpendicularly applied electric field. We carefully examine the bandgap's sensitivity to both magnitude of the applied field as well as separation between the graphene and hexagonal boron nitride layers. Features of the band structure are examined and configuration-dependent relationships between the field and bandgap are revealed and elucidated through the atom-projected density of states. These findings suggest the potential for opening and modulating a bandgap in graphene as high as several hundred meV.

We report density functional theory band structure calculations of graphene doped with group IV elements. A bandgap as high as 2.13 eV is calculated for a single layer of graphene doped with Si while Ge and Sn doping reduce this bandgap for equal doping concentrations. Bilayers of doped graphene are also studied and it is found that the bandgap of these materials is less than that of the single layer counterparts. Finally, a transverse electric field is applied to the doped bilayers and it is found that the bandgap is inversely proportional to the electric field strength in contrast to what has been observed in the case of pristine bilayers. Carrier effective masses were calculated and in general the effective masses of electrons and holes are found to be similar.

We experimentally demonstrate a high sensitivity pulsed laser vibrometer that is capable of detecting optically rough surfaces vibrating with the displacement value of 75 pm as well as its application as a laser microphone. By directing the probe light beam repeatedly onto the vibrating diaphragm and/or pressure sensing interface, the sensitivity of the pulsed laser vibrometer in detecting the displacement of the vibrating diaphragm is significantly improved down to an estimated value of less than 4 pm In this paper, we present the principles of operation of this new kind of laser microphone together with experimental validations.

We have observed Be diffusion in an AlGaAs/GaAs quantum‐well (QW) laser structure grown at ∼700 °C from the p‐AlGaAs cladding layer into the adjacent graded index (GRIN) AlGaAs and GaAs regions and beyond. This displaces the p/n junction from the AlGaAs/GaAs heterojunction. The Si dopant in n‐AlGaAs GRIN and cladding layers influences the diffusion of Be. When the GRIN regions on p and n sides are doped with Be and Si, respectively, the displacement of the p/n junction is significantly reduced. Oxygen, a common contaminant in AlGaAs irrespective of the growth technique, tends to accumulate at the inverted GaAs/AlGaAs heterointerface in the GRIN region. Furthermore, the Be‐doped Al0.6Ga0.4As cladding layer has an increased amount of O compared to its Si‐doped counterpart. In addition, cathodoluminescence (CL) intensity from the GaAs QW was more than an order of magnitude higher in structures with undoped GRIN regions compared to doped ones. The decreased CL and the increased amount of O in Be‐doped layers ...