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Pharmaceutical & Biopharmaceutical Development Services

EAG brings unparalleled expertise to the development and commercialization of small molecule drugs, biopharmaceuticals, antibody-drug conjugates (ADCs), drug-device combination…

EAG brings unparalleled expertise to the development and commercialization of small molecule drugs, biopharmaceuticals, antibody-drug conjugates (ADCs), drug-device combination products and other therapies. From designing IND-enabling studies to delivering full CMC analytical and QC support, we join your R&D team as a true partner. EAG scientists take time to understand both your commercial goals and the unique characteristics of your compound. We provide expert guidance to balance regulatory expectations with expediency and cost, and approach technical challenges with flexibility and resolve.

Materials Testing & Analysis

When it comes to understanding the physical structure, chemical properties and composition of materials, no scientific services company offers the breadth of experience, diversity…

When it comes to understanding the physical structure, chemical properties and composition of materials, no scientific services company offers the breadth of experience, diversity of analytical techniques of technical ingenuity of EAG. From polymers to composites, thin films to superalloys—we know how to leverage materials sciences to gain a competitive edge. At EAG, we don’t just perform testing, we drive commercial success—through thoughtfully designed investigations, technically superior analyses and expert interpretation of data.

Environmental Testing & Regulatory Compliance

Having helped develop the test methods that shape current regulatory guidelines, EAG chemists, biologists and toxicologists have evaluated the environmental impact of thousands of…

Having helped develop the test methods that shape current regulatory guidelines, EAG chemists, biologists and toxicologists have evaluated the environmental impact of thousands of active ingredients and formulations—from pesticides and pharmaceuticals to industrial chemicals and consumer products. Whether you are exploring “what if” scenarios, registering a new active ingredient or formulation, responding to a data call-in or seeking to understand the latest guidance, turn to EAG for technical excellence, sound advice, GLP-compliant study execution and expert interpretation.

Microelectronics Test & Engineering

Whether connecting the internet of things, guiding surgical lasers or powering the latest smart phone, integrated circuits and microelectronics touch nearly every aspect of human…

Whether connecting the internet of things, guiding surgical lasers or powering the latest smart phone, integrated circuits and microelectronics touch nearly every aspect of human life. In the world of technology, innovation and continuous improvement are imperatives—and being able to quickly and reliably test, debug, diagnose failures and take corrective action can make the difference between a doomed product launch and building a successful global brand. EAG offers you the world’s largest and most diverse collection of specialized analytical instrumentation, capacity to perform a variety of microelectronic tests in parallel, and the multi-disciplinary expertise required to draw true insight from data.

Custom Synthesis & Radiolabeling

No contract service provider has more experience performing custom synthesis and producing isotopically labeled compounds to support product development in life science, chemical…

No contract service provider has more experience performing custom synthesis and producing isotopically labeled compounds to support product development in life science, chemical and related industries than we do. From 14C and 3H radiolabeled clinical trial materials synthesized under cGMP, to stable-labeled active ingredients for metabolism and environmental fate/effects testing, turn to EAG. We have extensive experience with multi-step and other complex synthesis projects, and our comprehensive, in-house analytical services ensure quick turnaround of purity and structural confirmation.

Crop Biotechnology & Development

EAG combines biotechnology and protein characterization expertise with more than 50 years' experience analyzing chemical compounds in plant and environmental matrices to address…

EAG combines biotechnology and protein characterization expertise with more than 50 years’ experience analyzing chemical compounds in plant and environmental matrices to address the growing needs of the biotechnology crop industry. We offer a wide range of techniques required to fully characterize the event insertion and expressed proteins, as well as the various studies required to confirm the food, feed and environmental safety of products that represent the trait. From early-stage protein confirmation to GLP-compliant EDSP and allergenicity testing, we help you make faster, more informed development decisions and comply with evolving global regulations of genetically engineered crops.

Litigation Support & Expert Testimony

When you need solid science and investigative engineering to address product failures, inform legal strategy, protect intellectual property or address product liability disputes,…

When you need solid science and investigative engineering to address product failures, inform legal strategy, protect intellectual property or address product liability disputes, turn to EAG. We’ve provided technical consulting, analysis and expert testimony for hundreds of cases involving the aerospace, transportation, medical device, electronics, industrial and consumer product industries. Our team of experts understands the legal process and your need for responsiveness, effective communication, scientifically defensible opinion and confidentiality. From professional consulting to data review to trial preparation and expert witness testimony, ask EAG.

Techniques

Chromatography

Using an array of advanced separation techniques and innovative technology, we conduct highly precise analytical chromatography for various industries. Whether you want a closer…

Using an array of advanced separation techniques and innovative technology, we conduct highly precise analytical chromatography for various industries. Whether you want a closer look at the purity of your pharmaceutical or need to better understand an agrochemical’s components, EAG has the expertise to separate and evaluate any compound.

Mass Spectrometry

Need to evaluate the molecular structure of a compound or identify its origins? EAG knows how. With state-of-the-art tools, we can separate, vaporize and ionize the atoms and…

Need to evaluate the molecular structure of a compound or identify its origins? EAG knows how. With state-of-the-art tools, we can separate, vaporize and ionize the atoms and molecules in almost any pure or complex material to detect and obtain mass spectra of the components. We rely on decades of experience in mass spectrometry to provide our clients with precise analyses and the best detection limits.

Imaging

EAG is a world leader in high-resolution imaging down to the atomic level. We offer unmatched analytical know-how, generating extremely detailed surface and near surface images…

EAG is a world leader in high-resolution imaging down to the atomic level. We offer unmatched analytical know-how, generating extremely detailed surface and near surface images for various industries, from consumer electronics to nanotechnology. Using state-of-the-art equipment and innovative techniques, we conduct expert imaging to aid in failure analysis, dimensional analysis, process characterization, particle identification and more. If you want to investigate a material with angstrom scale resolution, you can count on EAG to get the job done quickly and precisely.

Spectroscopy

EAG offers a vast array of spectroscopic techniques to clients in various industries, from defense contractors to technology pioneers. We combine unparalleled expertise and…

EAG offers a vast array of spectroscopic techniques to clients in various industries, from defense contractors to technology pioneers. We combine unparalleled expertise and methodology with cutting-edge technology to analyze your organic, inorganic, metallic and composite materials for identification, compositional, structural and contaminant information. Whether you need expert spectroscopic analysis to improve your production process or to surmount a technical challenge, EAG is up to the task.

Physical/Chemical Characterization

Need to identify your unique material? Want to analyze the thermal properties of a sample, or measure the success of a process step? If it has to be done quickly and it has to be…

Need to identify your unique material? Want to analyze the thermal properties of a sample, or measure the success of a process step? If it has to be done quickly and it has to be done right, you can count on EAG. We offer a range of adaptable techniques and innovative methods to evaluate the physical and chemical characteristics of any compound. Our highly precise testing and analytical services will improve your production process, expedite R&D and help you conquer any technical challenge.

About

A Global Scientific Services Company

One of the most respected names in contract research and testing, EAG Laboratories is a global scientific services company operating at the intersection of science, technology and…

One of the most respected names in contract research and testing, EAG Laboratories is a global scientific services company operating at the intersection of science, technology and business. The scientists and engineers of EAG apply multi-disciplinary expertise, advanced analytical techniques and “we know how” resolve to answer complex questions that drive commerce around the world.

Our Customers

Science and technology transcend industry boundaries, and so does demand for EAG’s expertise. We partner with companies across a broad spectrum of high-tech, high-impact and…

Science and technology transcend industry boundaries, and so does demand for EAG’s expertise. We partner with companies across a broad spectrum of high-tech, high-impact and highly regulated industries. We help our customers innovate new and improved products, investigate manufacturing problems, perform advanced analyses to determine safety, efficacy and regulatory compliance, and protect their brands.

Our Company Culture

EAG’s corporate culture is firmly rooted in four guiding principles: “foster a growth mindset,” “find a better way,” “earn more loyal customers,” and “win…

EAG’s corporate culture is firmly rooted in four guiding principles: “foster a growth mindset,” “find a better way,” “earn more loyal customers,” and “win together.” Across all of our 20+ locations, you will find a true passion for science and the power of science to improve the world we live in. Hear what some of our ~1200 scientists, engineers and support personnel say about what it means to be part of EAG Laboratories.

Careers

EAG is growing, and we are always looking for talented, problem-solving oriented individuals to join our company. If you have a “we know how” spirit, we want to hear from you.…

EAG is growing, and we are always looking for talented, problem-solving oriented individuals to join our company. If you have a “we know how” spirit, we want to hear from you. Browse current openings now, and re-visit our careers page often.

How do you put science to work for you?

Scrutinizing VCSELs by SIMS

An advanced form of SIMS identifies dopants, impurities, compositions and thicknesses in various layers of VCSELs.

The VCSEL has several advantages over its edge-emitting cousin. Its strengths include a higher modulation speed, on-wafer testing and the emission of a symmetrical emission pattern that is oriented perpendicular to the surface. This form of emission, which is also produced when devices are configured in a two-dimensional array, is ideal for coupling into other optical components.

However, all these merits over the edge-emitting laser come at the expense of a more complex device architecture. With a VCSEL, resonator mirrors have to fulfil two roles: like an edge emitter, they have to control the extent of optical feedback and light output; but in addition, they also have to be electrically conducting, so that they can aid the injection of carriers from the contacts into the active region.

This set of requirements is often met by forming a stack of semiconductor layers, which have thicknesses that are carefully chosen to create a distributed Bragg reflector (DBR). To produce a high performance VCSEL, the DBR is formed from alternating layers with a sufficiently high refractive index contrast to realize high levels of reflection. Engineers must also ensure that the conductivity of the mirrors is sufficiently high to prevent current injection into the active region from causing excessive ohmic heating.

High-efficiency VCSELs are possible when these mirrors form part of a structure with a high degree of optical and electrical confinement. Such a device may be built from more than 200 layers, some of which can contain grading of both the doping level and the alloy composition. Growth of such a structure is very challenging, so process engineers support their efforts by using a variety of characterization techniques to uncover details associated with the epilayers, such as their thickness, doping and composition. While some approaches can only offer insights into a few of these characteristics, one is capable of delivering a great deal of detail about these structure – it is a variant of secondary ion mass spectrometry, known as Point-by-point CORrected SIMS, or PCOR-SIMS. Pioneered by our team at Evans Analytical Group, this technique can measure layer thickness, composition and doping profile more accurately than regular SIMS, where calibration with respect to alloy composition is not made at every data point (see Figure 1).

PCOR-SIMS provides depth profile of a full VCSEL structure
Figure 1. PCOR-SIMS pioneered by EAG Laboratories can provide a depth profile of a full VCSEL structure. All of the profiles were acquired in a single analysis. Boron profile marks the beginning of the substrate.

Our development of PCOR-SIMS can be traced back to the late 1990s when we were faced with acquiring accurate profiles for both dopants and matrix elements in SiGe materials. Previous to this time, it was commonly assumed that SIMS could not quantify matrix-level concentrations, and there was no way to change dopant sensitivities continuously based on matrix composition (because it was thought that SIMS could not measure matrix composition). While PCORSIMS did not require any instrument modifications, many test samples had to be fabricated and analyzed by other techniques. These samples formed the basis for the empirical relationships between sensitivity and concentration that are the underpinnings of the PCOR-SIMS methodology. In addition, other techniques, both nuclear and TEM-based, were used to verify the accuracy of the final PCOR-SIMS results.

One of the biggest challenges associated with the application of SIMS to the analysis of AlGaAs/GaAs VCSELs is that variations in aluminum content impact the sensitivity of aluminum. This means that the quantitative analysis of aluminum content is not straightforward. Complicating matters further, changes in alloy composition affect the sensitivity of the dopant species measured in the depth profile.

PCOR-SIMS addresses these issues by employing empirically derived analytical functions to correct for the well-known ‘SIMS matrix effect’, which comes into play when one deals with materials that are dissimilar in nature. In addition, this advanced variant of SIMS can account for changes in dopant sensitivity – these can be as much as a factor of two. The difference between traditional SIMS – where a single sensitivity is used in all layers – and PCOR-SIMS is illustrated in Figure 2. This shows the results of attempts to measure the silicon doping profile in an n-type DBR.

Graph shows how PCOR-SIMS measures silicon concentration independent of the proportion of aluminum in an n-DBR layer
Figure 2. The PCOR-SIMS technique pioneered by Evans Analytical Group is capable of accurate measurements of the silicon concentration, independent of the proportion of aluminum in an n-DBR layer.

Perfecting the VCSEL

Producing a very high performance VCSEL requires optimization of various aspects of the device, including: the aluminum composition and gradient between high and low refractive index mirror layers; the dopant profile between mirror layers; the composition of the aperture layer (assuming it is an oxide-confined VCSEL); the active layer impurity content; the aluminum grading on either side of the active layer; and, of course, the thicknesses of all of the layers within the structure.

An example of a PCOR-SIMS depth profile of a complete VCSEL structure is shown in Figure 1. This particular wafer uses a carbon-doped p-type AlGaAs DBR, a silicon-doped n-type AlGaAs DBR and an un-doped, low-aluminum AlGaAs active layer with multi-quantum well.

If the DBR is to provide good current injection, it must have a low electrical resistance. Realizing this in a manner that produces a good device is not trivial. Large energy band offsets between the low and high index semiconductor layers of the DBR can inhibit current flow, particularly for p-type DBRs – and the obvious solution of increasing the doping to trim resistance is not an option because this increases optical absorption.

A far better approach is to grade the AlGaAs composition at the interfaces, while varying the doping profiles at these points. In due course we will show how PCOR-SIMS is uniquely capable of measuring subtle alloy grading and interface doping profiles.

To obtain a high efficiency and low threshold current, the VCSEL has to confine both the carriers and the transverse optical modes. Today, this is often realized in AlGaAs VCSELs through the selective oxidation of an AlGaAs layer, which is near the active layer (this creates so-called ‘oxide-confined’ VCSELs). One challenge with this design is to control the oxidation of these layers: to form the confining aperture correctly and reproducibly, the composition of the Al0.98Ga0.02As layer must be controlled to 1 percent. Later in this article, we will demonstrate how PCOR-SIMS can aid the wafer grower, by measuring the composition of the AlGaAs layer with sufficient precision and accuracy.

Obviously, another pre-requisite for the successful growth of a VCSEL epiwafer is to accurately control the thicknesses of the many layers that make up a working device. Nowhere is this more important than in the DBR, where the thicknesses must be correct to tailor the optical properties of the mirrors.

However, one must not neglect the importance of obtaining the correct thickness for the cladding and active layers, because this is needed to place the lasing mode optimally with respect to the boundaries of the 1λ-optical cavity. As we will soon see, if the growth engineer turns to PCOR-SIMS, they can correctly measure the composition of each layer, and use this to determine the correct layer thicknesses.

Scrutinizing the structure

We have used our novel PCOR-SIMS technique to analyze a VCSEL structure with a carbon-doped p-type AlGaAs DBR, a silicon-doped n-type AlGaAs DBR and an un-doped, low aluminum AlGaAs active layer containing a multi-quantum well. In the remainder of this article, we will show how our technique can offer insights into the alloy composition profile, the DBR dopant profiles, and various details associated with the active layer.

As previously mentioned, grading the alloy composition between the low and high index layers can trim the resistance of the DBR. With our PCOR-SIMS technique, it is possible to hone in on this part of the structure − see Figure 3 for a higher-depth resolution profile of the top 200 nm of the sample – and reveal the compositional grading.

This occurs because the aluminum and gallium are not simply ‘switched on or off’, but varied in a precisely controlled manner to optimize the optical and electrical properties of the interfaces. Measurements with PCOR-SIMS have determined the aluminum content correctly over the entire range of composition, from 8 percent to 83 percent aluminum. The accuracy of these measurements has been verified against Standard Reference Material 2841 (Al0.1982±0.0014Ga0.8018As) from the National Institute of Standards and Technology and a Rutherford Backscattering Spectrometry calibrated, multicomposition AlGaAs reference material.

Further reductions in the resistance of the p-type DBR are possible by doping the mirrors with carbon, which has a sensitivity that is significantly affected by the alloy composition. However, with PCOR-SIMS we can correct for these effects at every data point, because the aluminum composition is measured for every carbon data point. Such an approach uncovers a high-concentration carbon-doping spike in some structures, which is near, but not exactly at, the interface between the low index layer with a higher aluminum content and the high index layer (see Figure 3).

Figure 3. Accurate carbon concentration and depth placement in AlGaAs layers with a graded composition.

We are confident that the placement of the carbon-doping spike is correct, because all of the profiles were acquired in the same analysis. Note that the low-level carbon dopant peaks may originate from a non-uniformity in doping, while the wafer was rotated during layer growth.

To provide current and optical confinement, producers of VCSELs tend to introduce a high-aluminum-content aperture, which is oxidized from the outside inwards. Halting the process at an appropriate point leaves an unoxidized ‘aperture’ through which current and light can pass. Obviously, to have a repeatable oxidation process, the rate of oxidation must not vary. This implies that there must be stringent compositional control and uniformity for the AlGaAs layer, because oxidation rates can vary by more than two orders of magnitude when aluminum content is increased from Al0.82Ga0.18As to Al1.0Ga 0As.

With PCOR-SIMS, the aluminum composition in high-aluminum- content AlGaAs layers, such as those used in forming aperture layers, can be determined with a high level of precision (see Figure 4). In these samples, the difference in aluminum content is only 1.8 percent of the of the Group III composition – or 0.9 percent of total atoms −but the spread in the measurement values of either film is much less. This degree of precision is crucial in perfecting these aperture layers.

This figure shows that PCOR-SIMS is capable of determining the composition of AIGaAs with high precision
Figure 4. PCOR-SIMS is capable of determining the composition of AlGaAs with high precision.

PCOR-SIMS can also offer insights into the structure of the active region (see Figure 5). It can reveal the aluminum profile, which varies on both sides of the active layer. There is grading from the p-type aperture layer, and also from the n-type DBR to the cladding layers, where it is followed by a steep drop in aluminum content, which is lower in the barrier layers immediately surrounding the AlGaAs active layer. A detailed picture of the active region is also helpful for assessing whether the lasing mode in the optical cavity is in the optimal position. The profile of the active region in Figure 5 also details the carbon doping for the active region and the mirror pairs nearby. By measuring carbon and silicon concentrations accurately in the n-type DBR with PCOR-SIMS, it is possible to determine the amount of p-type counter-doping that the inadvertent carbon contamination causes in the n-type layers.

This illustrates the depth profile of the active regions detail
Figure 5. Depth profile of the active region detail: (a) aperture layer composition; (b) gradient in cladding layer aluminum content; (c) cladding layer dopant concentration; (d) diffused doping in a multiquantum well. Note, the carbon profile is seen more clearly in Figure 2.

Another strength of PCOR-SIMS is its ability to profile unwanted contamination species. The most ubiquitous of these is oxygen, which can produce contamination spikes at the growth transition between the low index and the higher index layers of a p-type DBR (see Figure 6). Knowing the exact location of the oxygen spike in the growth sequence is often helpful when trying to isolate and eliminate the source of contamination.

Here we see that PCOR-SIMS can reveal oxygen contamination spike at DBR interfaces
Figure 6. PCOS-SIMS can reveal oxygen contamination spike at DBR interfaces.

Occasionally, VCSELs contain sulphur impurities, which are believed to affect performance. The level of sulphur is higher in p-DBRs than n-DBRs, because it tracks the proportion of aluminum content (see Figure 7). The peak in the upper graded AlGaAs cladding layer is easier to spot in higher resolution reanalysis of the active region (Figure 8).

This shows sulphur impurities which may degrade VCSEL performance
Figure 7. Sulphur impurities, which may degrade VCSEL performance, can be detected in many layers of this VCSEL structure.

Here we see a peaking sulpher impurity detected in upper AIGaAs cladding layer
Figure 8. A peaking sulphur impurity is detected in upper AlGaAs cladding layer.

Determining the correct layer thickness with conventional SIMS is not easy, because changes in alloy composition alter the sputtering rate at the surface. If no corrections are made, the plotted layer thickness can be in error by 20 percent for an AlGaAs VCSEL (see Figure 9).

This is a depth profile of an AIGaAs DBR layer, showing the PCOR-SIMS layer thickness correction
Figure 9. A depth profile of an AlGaAs DBR layer, showing the PCORSIMS layer-thickness correction.

With PCOR-SIMS this weakness is addressed with an empirically derived sputtering-rate function. This determines the instantaneous sputtering rate for each data point based on the measured aluminum content − or indium content for InGaAs active layers − for that data point. Armed with this approach, compensation corrections are made for variations in sputtering rate throughout the VCSEL.

Our development of an advanced form of SIMS has opened up the capabilities of this technique so that it is no longer limited to impurity and dopant analyses of semiconductor materials. This effort has enabled PCOR-SIMS to be the most valuable tool for the growers of VCSELs: It can used for various important tasks, including uncovering doping levels in graded layers and delivering precise values for the aluminum composition in AlGaAs aperture layers.

Article originally appeared in Compound Semiconductor, Volume 20, Issue 3 2014

Authors: Temel Buyuklimanli, Charles Magee, Jeffrey Serfass and Jeffrey Kipnis, EAG Laboratories