Outcomes of decompressive craniectomy in adults with severe traumatic brain injury: the Groote Schuur Hospital experience

Includes bibliographical references.Object: The aim of this study was to assess outcome following decompressive craniectomy in adults with severe traumatic brain injury (TBI) in a South African neurosurgical unit. Methods: During a 78 month period (January 2005 – June 2011), 76 patients that underwent decompressive craniectomy for TBI in an attempt to lower raised intracranial pressure (ICP) were reviewed . All were older than 14 years and mass lesions were included. Thirty nine point four percent of the patients sustained blunt, low velocity injuries to the head and 19% were involved in motor vehicle accidents. Unilateral hemi-craniectomies were carried out in 81% of patients and 54 (75%) were done as primary decompressive craniectomies. Survivors were followed up for a period of at least six months and functional outcomes were measured using the Glasgow outcomes score. To simplify outcomes the patients were then dichotomised into outcome groups of good (GOS 4 and 5 ), and poor (GOS 1- 3). Results: At six months follow up 24 patients (33.3%) had a good outcome (GOS 4 or 5) and 48 patients (66.7%) had a poor outcome (GOS 1- 3). 32 patients (44.4%) died (GOS 1). There were 16 survivors in the poor group. Sixty percent o f survivors had a good outcome after decompressive craniectomy. Eighteen patients underwent secondary decompressive craniectomies and 54 (75%) primary decompressive craniectomies. Thirty - five percent of patients that underwent primary decompressive cranie ctomy had a good outcome, versus 38% in the secondary decompression group. Mortality was slightly higher in the primary decompression group (43%) than the secondary group (33%) . Factors that showed significant correlation with outcome were age, admission GCS and good response of ICP to decompressive craniectomy. Complications were encountered in 18% of patients with sepsis being the most common (11%). Conclusion: Decompressive craniectomy was associated with a functional outcome that was better than exp ected in patients with severe TBI and should still form part of salvage therapy in adults with TBI and elevated ICP

Determination of Sapphire Off‐Cut and Its Influence on the Morphology and Local Defect Distribution in Epitaxially Laterally Overgrown AlN for Optically Pumped UVC Lasers

Herein, a systematic study of the morphology and local defect distribution in epitaxially laterally overgrown (ELO) AlN on c‐plane sapphire substrates with different off‐cut angles ranging from 0.08° to 0.23° is presented. Precise measurements of the off‐cut angle α, using a combination of optical alignment and X‐ray diffraction with an accuracy of ±5° for the off‐cut direction and ±0.015° for the off‐cut angle, are carried out. For ELO AlN growth, a transition from step flow growth at α  0.14° is observed. Furthermore, the terraces of the step‐bunched surface exhibit curved steps. An analysis of the local defect distribution by scanning transmission electron microscopy and a comparison with atomic force microscopy reveal a bunching of defects in line with the ELO pattern and a roughening of step edges in highly defective regions. In addition, a reduction in the threshold excitation power density for optically pumped ultraviolet‐C (UVC) lasers with smooth surface morphologies is observed.TU Berlin, Open-Access-Mittel - 201

Thin-film flip-chip UVB LEDs realized by electrochemical etching

We demonstrate a thin-film flip-chip (TFFC) light-emitting diode (LED) emitting in the ultraviolet B (UVB) at 311 nm, where substrate removal has been achieved by electrochemical etching of a sacrificial Al0.37Ga0.63N layer. The electroluminescence spectrum of the TFFC LED corresponds well to the as-grown LED structure, showing no sign of degradation of structural and optical properties by electrochemical etching. This is achieved by a proper epitaxial design of the sacrificial layer and the etch stop layers in relation to the LED structure and the electrochemical etch conditions. Enabling a TFFC UV LED is an important step toward improving the light extraction efficiency that limits the power conversion efficiency in AlGaN-based LEDs

Athermalization of the Lasing Wavelength in Vertical-Cavity Surface-Emitting Lasers

A concept for vertical-cavity surface-emitting lasers (VCSELs) is proposed and demonstrated to obtain a lasing wavelength with unprecedented temperature stability. The concept is based on incorporating a dielectric material with a negative thermo-optic coefficient, dn/dT, in the distributed Bragg reflectors (DBRs) to compensate the positive dn/dT of the semiconductor cavity. In a short cavity, the optical field has a significant overlap with the DBRs, and the redshift of the lasing wavelength caused by the semiconductor cavity can be compensated by the negative dn/dT of the DBRs. Here, proof of this concept is presented for optically-pumped VCSELs emitting at 310 nm, demonstrating a lasing wavelength that even blueshifts by less than 0.1\ua0nm over an 80 \ub0C range with a maximum slope of –3.4\ua0pm K−1. This is to be compared with a redshift of 1–1.5\ua0nm over the same temperature range reported for III-nitride blue-emitting VCSELs. Furthermore, this method can also be implemented in VCSELs with longer cavity lengths by including a dielectric layer between the semiconductor and the DBR. The approach used here to obtain a temperature-stable lasing wavelength is generic and can therefore be applied to VCSELs in all material systems and lasing\ua0wavelengths

Indium incorporation in quaternary Inx Aly Ga1-x-y N for UVB-LEDs

Consistent studies of the quaternary composition are rare as it is impossible to fully determine the quaternary composition by X-ray diffraction or deduce it from that of ternary alloys. In this paper we determined the quaternary composition by wavelength dispersive X-ray spectroscopy of Inx Aly layers grown by metal organic vapor phase epitaxy. Further insights explaining the peculiarities of Inx Aly Ga1-x-yN growth in a showerhead reactor were gained by simulations of the precursor decomposition, gas phase adduct formation and indium incorporation including desorption. The measurements and simulations agree very well showing that the indium incorporation in a range from 0% to 2% is limited by desorption which is enhanced by the compressive strain to the relaxed Al0.5Ga0.5N buffer layer as well as indium incorporation into AlN particles forming in the gas phase. Utilizing Inx Aly Ga1-x-yN layers containing 2% of indium for multiple quantum wells (MQWs), it was possible to show an almost five times higher photoluminescence intensity of InAlGaN MQWs in comparison to AlGaN MQWs

Increased Light Extraction of Thin-Film Flip-Chip UVB LEDs by Surface Texturing

Ultraviolet light-emitting diodes (LEDs) suffer from a low wall-plug efficiency, which is to a large extent limited by the poor light extraction efficiency (LEE). A thin-film flip-chip (TFFC) design with a roughened N-polar AlGaN surface can substantially improve this. We here demonstrate an enabling technology to realize TFFC LEDs emitting in the UVB range (280-320 nm), which includes standard LED processing in combination with electrochemical etching to remove the substrate. The integration of the electrochemical etching is achieved by epitaxial sacrificial and etch block layers in combination with encapsulation of the LED. The LEE was enhanced by around 25% when the N-polar AlGaN side of the TFFC LEDs was chemically roughened, reaching an external quantum efficiency of 2.25%. By further optimizing the surface structure, our ray-tracing simulations predict a higher LEE from the TFFC LEDs than flip-chip LEDs and a resulting higher wall-plug efficiency

Electrochemical etching of AlGaN for the realization of thin-film devices

Heterogeneously integrated AlGaN epitaxial layers will be essential for future optical and electrical devices like thin-film flip-chip ultraviolet (UV) light-emitting diodes, UV vertical-cavity surface-emitting lasers, and high-electron mobility transistors on efficient heat sinks. Such AlGaN-membranes will also enable flexible and micromechanical devices. However, to develop a method to separate the AlGaN-device membranes from the substrate has proven to be challenging, in particular, for high-quality device materials, which require the use of a lattice-matched AlGaN sacrificial layer. We demonstrate an electrochemical etching method by which it is possible to achieve complete lateral etching of an AlGaN sacrificial layer with up to 50% Al-content. The influence of etching voltage and the Al-content of the sacrificial layer on the etching process is investigated. The etched N-polar surface shows the same macroscopic topography as that of the as-grown epitaxial structure, and the root-mean square roughness is 3.5 nm for 1 \ub5m x 1 \ub5m scan areas. Separated device layers have a well-defined thickness and smooth etched surfaces. Transferred multi-quantum-well structures were fabricated and investigated by time-resolved photoluminescence measurements. The quantum wells showed no sign of degradation caused by the thin-film process

Analysis of doping concentration and composition in wide bandgap AlGaN:Si by wavelength dispersive x-ray spectroscopy

Detailed knowledge of the dopant concentration and composition of wide band gap AlxGa1−xN layers is of crucial importance for the fabrication of ultra violet light emitting diodes. This paper demonstrates the capabilities of wavelength dispersive x-ray (WDX) spectroscopy in accurately determining these parameters and compares the results with those from high resolution x-ray diffraction (HR-XRD) and secondary ion mass spectrometry (SIMS). WDX spectroscopy has been carried out on different silicon-doped wide bandgap AlxGa1−xN samples (x between 0.80 and 1). This study found a linear increase in the Si concentration with the SiH4/group-III ratio, measuring Si concentrations between 3×10 18 cm−3 and 2.8×10 19 cm−3, while no direct correlation between the AlN composition and the Si incorporation ratio was found. Comparison between the composition obtained by WDX and by HR-XRD showed very good agreement in the range investigated, while comparison of the donor concentration between WDX and SIMS found only partial agreement, which we attribute to a number of effects.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeBMBF, 13N12587, Verbundprojekt: Photonische Plattformtechnologie zur ultrasensitiven und hochspezifischen biochemischen Sensorik auf Basis neuartiger UV-LEDs (UltraSens) - Teilvorhaben: Design, Wachstum und Charakterisierung von UV-C-LEDsBMBF, 03ZZ0105B, Zwanzig20 - Advanced UV for Life - Verbundvorhaben - UV-B effizient; TP2: Optimierung der Epitaxiestruktur und Epitaxieprozesse für den aktiven Bereich, LED-Simulation und ChipdesignBMBF, 03ZZ0103, Zwanzig20 - Advanced UV for Life - Ertüchtigung der Prozesskette für UV-LED

Low-Threshold AlGaN-based UVB VCSELs enabled by post-growth cavity detuning

The performance of vertical-cavity surface-emitting lasers (VCSELs) is strongly dependent on the spectral detuning between the gain peak and the resonance wavelength. Here, we use angle-resolved photoluminescence spectroscopy to investigate the emission properties of AlGaN-based VCSELs emitting in the ultraviolet-B spectral range with different detuning between the photoluminescence peak of the quantum-wells and the resonance wavelength. Accurate setting of the cavity length, and thereby the resonance wavelength, is accomplished by using doping-selective electrochemical etching of AlGaN sacrificial layers for substrate removal combined with deposition of dielectric spacer layers. By matching the resonance wavelength to the quantum-wells photoluminescence peak, a threshold power density of 0.4 MW/cm2 was achieved, and this was possible only for smooth etched surfaces with a root mean square roughness below 2 nm. These results demonstrate the importance of accurate cavity length control and surface smoothness to achieve low-Threshold AlGaN-based ultraviolet VCSELs

A 310 nm Optically Pumped AlGaN Vertical-Cavity Surface-Emitting Laser

Ultraviolet light is essential for disinfection, fluorescence excitation, curing, and medical treatment. An ultraviolet light source with the small footprint and excellent optical characteristics of vertical-cavity surface-emitting lasers (VCSELs) may enable new applications in all these areas. Until now, there have only been a few demonstrations of ultraviolet-emitting VCSELs, mainly optically pumped, and all with low Al-content AlGaN cavities and emission near the bandgap of GaN (360 nm). Here, we demonstrate an optically pumped VCSEL emitting in the UVB spectrum (280-320 nm) at room temperature, having an Al0.60Ga0.40N cavity between two dielectric distributed Bragg reflectors. The double dielectric distributed Bragg reflector design was realized by substrate removal using electrochemical etching. Our method is further extendable to even shorter wavelengths, which would establish a technology that enables VCSEL emission from UVA (320-400 nm) to UVC (<280 nm)