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Dr Konstanze Hild


Teaching Fellow

Academic and research departments

Advanced Technology Institute.

Biography

Biography

Since 2016 working as a Teaching Fellow in the Physics Department.

From 2016-2018 also working as a project facilitator helping researchers to develop new techniques to address to antimicrobial resistance challenge. 

From January 2011 working as a Research Fellow on the optical characterisation of bismuth containing semiconductors. Applications for this range from more temperature sensitive telecommunications lasers to novel solar cell designs. Recently also getting involved into research of solid state lighting, not only from the technology side but also with respect to the human response.

2005-2008 Research Assistant (University of Surrey) working on GaAsSb based lasers for emission at 1.3 microns.

2000-2003 University of Surrey. The PhD work (Surrey 2003) concerned the spectroscopy (photomodulated reflectance) and device measurements of Resonant Cavity LEDs emitting at 650nm.

1994-2000 Universität Dortmund. Working on the spectroscopy of single excitonic states in II-VI semiconductor structures for the Diplom obtained in January 2000.

Research interests

Improving the performance of LEDs and lasers.

Influence of light on humans.

New ways of addressing the antimicrobial resistance challenge.

Teaching

Level 1 Laboratories

Level 1 Small group tutorials

Level 1 Properties of Matter

Level 2 Laboratories

My publications

Publications

Bonmati-Carrion MA, Hild K, Isherwood C, Sweeney SJ, Revell VL, Skene DJ, Rol MA, Madrid JA (2016) Relationship between Human Pupillary Light Reflex and Circadian System Status, PLoS One 11 (9) e0162476 Public Library of Science (PLoS)
Intrinsically photosensitive retinal ganglion cells (ipRGCs), whose photopigment melanopsin
has a peak of sensitivity in the short wavelength range of the spectrum, constitute a common
light input pathway to the olivary pretectal nucleus (OPN), the pupillary light reflex
(PLR) regulatory centre, and to the suprachiasmatic nuclei (SCN), the major pacemaker of
the circadian system. Thus, evaluating PLR under short wavelength light (»max 500 nm)
and creating an integrated PLR parameter, as a possible tool to indirectly assess the status
of the circadian system, becomes of interest. Nine monochromatic, photon-matched light
stimuli (300 s), in 10 nm increments from »max 420 to 500 nm were administered to 15
healthy young participants (8 females), analyzing: i) the PLR; ii) wrist temperature (WT) and
motor activity rhythms (WA), iii) light exposure (L) pattern and iv) diurnal preference (Horne-
Östberg), sleep quality (Pittsburgh) and daytime sleepiness (Epworth). Linear correlations
between the different PLR parameters and circadian status index obtained from WT, WA
and L recordings and scores from questionnaires were calculated. In summary, we found
markers of robust circadian rhythms, namely high stability, reduced fragmentation, high
amplitude, phase advance and low internal desynchronization, were correlated with a
reduced PLR to 460?490 nm wavelengths. Integrated circadian (CSI) and PLR (cp-PLR)
parameters are proposed, that also showed an inverse correlation. These results demonstrate,
for the first time, the existence of a close relationship between the circadian system
robustness and the pupillary reflex response, two non-visual functions primarily under melanopsin-ipRGC
input.
Batool Z, Hild K, Hosea TJC, Lu X, Tiedje T, Sweeney SJ (2012) The electronic band structure of GaBiAs/GaAs layers: Influence of strain and band anti-crossing, JOURNAL OF APPLIED PHYSICS 111 (11) ARTN 113108 AMER INST PHYSICS
Batool Z, Chatterjee S, Chernikov A, Duzik A, Fritz R, Gogineni C, Hild K, Hosea TJC, Imhof S, Johnson SR, Jiang Z, Jin S, Koch M, Koch SW, Kolata K, Lewis RB, Lu X, Masnadi-Shirazi M, Millunchick JM, Mooney PM, Riordan NA, Rubel O, Sweeney SJ, Thomas JC, Thränhardt A, Tiedje T, Volz K (2013) Bismuth-containing III-V semiconductors: Epitaxial growth and physical properties, pp. 139-158
Hild K, Sweeney SJ, Marko IP, Jin SR, Johnson SR, Chaparro SA, Yu S, Zhang Y-H (2007) Temperature and pressure dependence of carrier recombination processes in GaAsSb/GaAs quantum well lasers, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (1) pp. 197-202 WILEY-V C H VERLAG GMBH
Hossain N, Marko IP, Jin SR, Hild K, Sweeney SJ, Lewis RB, Beaton DA, Tiedje T (2012) Recombination mechanisms and band alignment of GaAs1-xBix/GaAs light emitting diodes, APPLIED PHYSICS LETTERS 100 (5) ARTN 051105
Marko I, Sweeney S, Hild K (2016) Temperature stable mid-infrared GaInAsSb/GaSb Vertical Cavity Surface Emitting Lasers (VCSELs), Scientific Reports 6 19595 Nature Publishing Group
GaInAsSb/GaSb based quantum well vertical cavity surface emitting lasers (VCSELs) operating in mid-infrared spectral range between 2 and 3 micrometres are of great importance for low cost gas monitoring applications. This paper discusses the efficiency and temperature sensitivity of the VCSELs emitting at 2.6 ¼m and the processes that must be controlled to provide temperature stable operation. We show that non-radiative Auger recombination dominates the threshold current and limits the device performance at room temperature. Critically, we demonstrate that the combined influence of non-radiative recombination and gain peak ? cavity mode de-tuning determines the overall temperature sensitivity of the VCSELs. The results show that improved temperature stable operation around room temperature can only be achieved with a larger gain peak ? cavity mode de-tuning, offsetting the significant effect of increasing non-radiative recombination with increasing temperature, a physical effect which must be accounted for in mid-infrared VCSEL design.
Ikyo AB, Marko IP, Hild K, Adams AR, Arafin S, Amann M-C, Sweeney SJ Temperature stable mid-infrared GaInAsSb/GaSb Vertical Cavity Surface Emitting Lasers (VCSELs), NATURE PUBLISHING GROUP
Usman M, Broderick CA, Batool Z, Hild K, Hosea TJC, Sweeney SJ, O'Reilly EP (2013) Impact of alloy disorder on the band structure of compressively strained GaBixAs1-x, Physical Review B - Condensed Matter and Materials Physics 87 (11)
The incorporation of bismuth (Bi) in GaAs results in a large reduction of the band gap energy (Eg) accompanied with a large increase in the spin-orbit splitting energy (SO), leading to the condition that SO>Eg, which is anticipated to reduce hot-hole producing Auger recombination losses whereby the energy and momentum of a recombining electron-hole pair are given to a second hole which is excited into the spin-orbit band. We theoretically investigate the electronic structure of experimentally grown GaBixAs1-x samples on (100) GaAs substrates by directly comparing our data with room temperature photomodulated reflectance (PR) measurements. Our atomistic theoretical calculations, in agreement with the PR measurements, confirm that Eg is equal to SO for xH 9%. We then theoretically probe the inhomogeneous broadening of the interband transition energies as a function of the alloy disorder. The broadening associated with spin-split-off transitions arises from conventional alloy effects, while the behavior of the heavy-hole transitions can be well described using a valence band-anticrossing model. We show that for the samples containing 8.5% and 10.4% Bi the difficulty in identifying a clear light-hole-related transition energy from the measured PR data is due to the significant broadening of the host matrix light-hole states as a result of the presence of a large number of Bi resonant states in the same energy range and disorder in the alloy. We further provide quantitative estimates of the impact of supercell size and the assumed random distribution of Bi atoms on the interband transition energies in GaBixAs1-x. Our calculations support a type-I band alignment at the GaBixAs 1-x/GaAs interface, consistent with recent experimental findings. © 2013 American Physical Society.
Marko IP, Ludewig P, Bushell ZL, Jin SR, Hild K, Batool Z, Reinhard S, Nattermann L, Stolz W, Volz K, Sweeney SJ (2014) Physical properties and optimization of GaBiAs/(Al)GaAs based near-infrared laser diodes grown by MOVPE with up to 4.4% Bi, Journal of Physics D: Applied Physics 47 (34)
This paper reports on progress in the development of GaAsBi/(Al)GaAs based lasers grown using metal-organic vapour phase epitaxy and focuses on the underlying processes governing their efficiency and temperature dependence. Room temperature lasing has been achieved in devices with 2.2% Bi and lasing in devices with 4.4% Bi was observed up to 180 K. We show that the device performance can be improved by optimizing both electrical and optical confinement in the laser structures. Analysis of the temperature dependence of the threshold current together with pure spontaneous emission and high hydrostatic pressure measurements indicate that device performance is currently dominated by non-radiative recombination through defects (>80% of the threshold current at room temperature in 2.2% Bi samples) and that to further improve the device performance and move towards longer wavelengths for optical telecommunications (1.3-1.5 ¼ m) further effort is required to improve and optimize material quality. © 2014 IOP Publishing Ltd.
Hild K, Sweeney SJ, Jin SR, Healy SB, O'Rellly EP, Johnson SR, Wang J-B, Zhang Y-H (2007) Band alignment and carrier recombination in GaAsSb/GaAs quantum wells, Physics of Semiconductors, Pts A and B 893 pp. 1431-1432 AMER INST PHYSICS
Sweeney SJ, Hild K, Marko IP, Yu S-Q, Johnson SR, Zhang Y-H (2008) Thermal characteristics of 1.3 mu m GaAsSb/GaAs-based Edge- and Surface-emitting Lasers, 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE pp. 83-84 IEEE
Hild K, Sale TE, Hosea TJC, Hirotani M, Mizuno Y, Kato T (2001) Influence of quantum well and cavity features on the spectral, angle- and temperature-dependent emission of 650 mn resonant cavity LEDs, PHYSICA STATUS SOLIDI A-APPLIED RESEARCH 188 (3) pp. 937-941 WILEY-V C H VERLAG GMBH
Sweeney SJ, Marko IP, Jin SR, Hild K, Batool Z, Ludewig P, Natterman L, Bushell Z, Stolz W, Volz K, Broderick CA, Usman M, Harnedy PE, Oreilly EP, Butkute R, Pacebutas V, Geiutis A, Krotkus A (2014) Electrically injected GaAsBi quantum well lasers, Conference Digest - IEEE International Semiconductor Laser Conference pp. 80-81
© 2014 IEEE.GaAsBi QWs have the potential to remove inherent recombination losses thereby increasing the efficiency and reducing the temperature sensitivity of near-infrared telecommunications lasers. GaAsBi QW lasers are reported and prospects for 1550nm operation are discussed.
Hild K, Sale TE, Hirotani M, Mizuno Y, Kato T (2003) Leakage current and self-heating in 650 nm resonant-cavity LEDs, Conference on Lasers and Electro-Optics Europe - Technical Digest
This paper investigates the contributions of leakage current and self-heating to the temperature sensitivity. The amount of self-heating and leakage current is estimated and plotted for a constant light output with increasing temperature for both CW and pulsed operation, and the radiative current density for 650 nm emitting GaInP based resonant cavity light emitting diodes (RCLEDs) is calculated using a drift diffusion model (DDM).The model simulates the distribution of charge carriers within the structure and their recombination mechanisms. The radiative current in GaInP quantum wells is also extracted and plotted. © 2003 IEEE.
Sweeney SJ, Batool Z, Hild K, Jin SR, Hosea TJC (2011) The Potential Role of Bismide Alloys in Future Photonic Devices, 13TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS IEEE
In a similar manner to the dilute nitrides, the incorporation of Bismuth in semiconductors such as GaAs is predicted to lead to a band-anti-crossing effect (in the valence band) causing a large band gap bowing. In addition, the large size of Bismuth atoms gives rise to a large spin-orbit splitting. This opens-up interesting new possibilities for efficient photonic devices, such as near- and mid-infrared lasers which are more thermally stable and less susceptible to losses compared to conventional InP-based devices. Since Bismuth principally influences the valence band, while nitrogen influences the conduction band, combining Bismuth and Nitrogen in III-V alloys offers huge potential for engineering the conduction and valence band offsets, the band gap and spin-orbit splitting, with wide scope for the design of photonic devices.
Blume G, Hild K, Marko IP, Hosea TJC, Yu SQ, Chaparro SA, Samal N, Johnson SR, Zhang YH, Sweeney SJ (2012) Cavity mode gain alignment in GaAsSb-based near-infrared vertical cavity lasers studied by spectroscopy and device measurements, Journal of Applied Physics 112 (3)
We present a combination of spectroscopy and device measurements on GaAsSb/GaAs vertical-cavity surface-emitting laser (VCSEL) structures to determine the temperature at which the wavelength of the VCSEL cavity mode (CM) aligns with that of the quantum well (QW) ground-state transition (GST), and therefore the gain peak. We find that, despite the achievement of room temperature (RT) continuous wave lasing in VCSEL devices, the QW transition and the CM are actually slightly misaligned at this temperature; room temperature electroluminescence measurements from a cleaved edge of the VCSEL wafer indicate that the 300 K QW GST energy is at 0.975 ± 0.005 eV, while the CM measured in the VCSEL surface reflectivity spectra is at 0.9805 ± 0.0002 eV. When the wafer sample is cooled, the CM and QW GST can be brought into alignment at 270 ± 10 K, as confirmed by temperature-dependent electro-modulated reflectance (ER) and edge-electroluminescence spectroscopic studies. This alignment temperature is further confirmed by comparing the temperature dependence of the emission energy of a fabricated VCSEL device with that of an edge-emitting laser structure with a nominally identical active region. The study suggests that for further device improvement, the room temperature CM and QW GST energies should be more closely matched and both designed to a smaller energy of about 0.95 eV, somewhat closer to the 1.31 ¼m target. The study amply demonstrates the usefulness of non-destructive ER characterisation techniques in VCSEL manufacturing with GaAsSb-based QWs. © 2012 American Institute of Physics.
Sweeney SJ, Hild K, Jin S (2013) The potential of GaAsBiN for multi-junction solar cells, Conference Record of the IEEE Photovoltaic Specialists Conference pp. 2474-2478
The use of multiple connected absorbing junctions (MJ-solar cells) is currently the best approach to maximize the efficiency of solar cells. Increasing the number of junctions leads to a larger theoretical efficiency. To achieve this requires the development of materials appropriate band gaps, which can be grown to a sufficient thickness to absorb light while current matched to other junctions and at the same time minimizing strain and defect generation by lattice matching. We report on modelling of the quaternary alloy GaAsBiN which has the potential to cover a wide range of band gaps below 1.42eV. In addition, this material can also be grown completely lattice matched onto GaAs or Ge with controllable band offsets which makes it very attractive for solar cell applications. © 2013 IEEE.
Marko IP, Jin SR, Hild K, Batool Z, Bushell ZL, Ludewig P, Stolz W, Volz K, Butkute R, Pacebutas V, Geizutis A, Krotkus A, Sweeney SJ (2015) Properties of hybrid MOVPE/MBE grown GaAsBi/GaAs based near-infrared emitting quantum well lasers, SEMICONDUCTOR SCIENCE AND TECHNOLOGY 30 (9) ARTN 094008 IOP PUBLISHING LTD
Ikyo BA, Marko IP, Hild K, Adams AR, Arafin S, Amann MC, Sweeney SJ (2013) The effect of hole leakage and auger recombination on the temperature sensitivity of GaInAsSb/GaSb mid-infrared lasers, Optics InfoBase Conference Papers
Hild K, Marko IP, Johnson SR, Yu S-Q, Zhang Y-H, Sweeney SJ (2011) Influence of de-tuning and non-radiative recombination on the temperature dependence of 1.3 mu m GaAsSb/GaAs vertical cavity surface emitting lasers, APPLIED PHYSICS LETTERS 99 (7) ARTN 071110 AMER INST PHYSICS
Chai GMT, Hosea TJC, Fox NE, Hild K, Ikyo AB, Marko IP, Sweeney SJ, Bachmann A, Arafin S, Amann M-C (2014) Characterization of 2.3 mu m GaInAsSb-based vertical-cavity surface-emitting laser structures using photo-modulated reflectance, JOURNAL OF APPLIED PHYSICS 115 (1) ARTN 013102 AMER INST PHYSICS
Hild K, Batool Z, Jin SR, Hossain N, Marko IP, Hosea TJC, Lu X, Tiedje T, Sweeney SJ (2013) Auger Recombination Suppression And Band Alignment In GaAsBi/GaAs Heterostructures, PHYSICS OF SEMICONDUCTORS 1566 pp. 488-489 AMER INST PHYSICS
Hild K, Sale TE, Hosea TJC, Hirotani M, Hirotani M, Kato T (2001) Spectral and thermal properties of red AlGaInP RCLEDs for polymer optical fibre applications, IEE PROCEEDINGS-OPTOELECTRONICS 148 (5-6) pp. 220-224 IEE-INST ELEC ENG
Sale TE, Hild K, Hosea TJC, Hirotani M, Kato Y (2004) Reflectivity fitting for accurate thickness and compositional determination in RCLEDs, LIGHT -EMITTING DIODES: RESEARCH, MANUFACTURING, AND APPLICATIONS VIII 5366 pp. 191-199 SPIE-INT SOC OPTICAL ENGINEERING
Marko IP, Batool Z, Hild K, Jin SR, Hossain N, Hosea TJC, Petropoulos JP, Zhong Y, Dongmo PB, Zide JMO, Sweeney SJ (2012) Temperature and Bi-concentration dependence of the bandgap and spin-orbit splitting in InGaBiAs/InP semiconductors for mid-infrared applications, Applied Physics Letters 101 (22)
Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, Eg, and spin-orbit splitting, ”SO, respectively. The possibility of achieving ”SO > Eg and a reduced temperature (T) dependence for Eg are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure E g(x, T) and ”SO (x, T) in In0.53Ga 0.47BixAs1-x/InP samples for 0 x 0.039 by various complementary optical spectroscopic techniques. While we find no clear evidence of a decreased dEg/dT (H0.34 ± 0.06 meV/K in all samples) we find ”SO > Eg for x > 3.3-4.3. The predictions of a valence band anti-crossing model agree well with the measurements. © 2012 American Institute of Physics.
Hossain N, Hild K, Jin S, Sweeney SJ, Yu S-Q, Johnson SR, Ding D, Zhang Y-H (2010) Role of growth temperature on the physical characteristics of GaAsSb/GaAs QW lasers, 23rd Annual Meeting of the IEEE Photonics Society pp. 59-60 IEEE
Thermally activated carrier leakage via defects is found to be very sensitive to the growth temperature of GaAsSb quantum wells. Optimization of the growth temperature leads to a low Jth/QW of 138A/cm2 at RT.
Bushell ZL, Ludewig P, Knaub N, Batool Z, Hild K, Stolz W, Sweeney SJ, Volz K (2014) Growth and characterisation of Ga(NAsSi) alloy by metal-organic vapour phase epitaxy, JOURNAL OF CRYSTAL GROWTH 396 pp. 79-84 ELSEVIER SCIENCE BV
Hossain N, Hild K, Jin SR, Sweeney SJ, Yu S-Q, Johnson SR, Ding D, Zhang Y-H (2010) Influence of device structures on carrier recombination in GaAsSb/GaAs QW lasers, Proceedings of Photonics Global Conference
We investigate the temperature and pressure dependence of carrier recombination processes occurring in various GaAsSb/GaAs QW laser structures grown under similar growth conditions. Thermally activated carrier leakage via defects is found to be very sensitive to the strain induced interface imperfections. Nonradiative recombination is found to be sensitive to the number of QWs. A strain compensated MQW structure leads to a reduced contribution of non-radiative recombination to the threshold current density (Jth) and a high characteristic temperature (T0) of 73K at room temperature.
Hild K, Sale TE, Sweeney SJ, Hirotani M, Mizuno Y, Kato T (2004) Modulation speed resonant-cavity and leakage current in 650 nm light emitting diodes, IEE PROCEEDINGS-OPTOELECTRONICS 151 (2) pp. 94-97 IEE-INST ELEC ENG
Hosea TJC, Marko IP, Batool Z, Hild K, Jin SR, Hossain N, Chai GMT, Sweeney SJ, Petropoulos JP, Zhong Y, Dongmo PB, Zide JMO (2012) InGaBiAs/InP semiconductors for mid-infrared applications: Dependence of bandgap and spin-orbit splitting on temperature and bismuth content, ICP 2012 - 3rd International Conference on Photonics 2012, Proceedings pp. 154-158
Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, Eg, and spin-orbit splitting, ”SO, respectively. The possibility of achieving ”SO>Eg and a reduced temperature (T) dependence for Eg are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure E g(x, T) and ”SO(x, T) in In0.53Ga 0.47BixAs1-x/InP samples for 0dxd0.032 by optical spectroscopy. While we find no clear evidence of a decreased dE g/dT (H0.33±0.07meV/K in all samples) we find ”SO>Eg for x>3.3-4.3%. The predictions of a valence band anti-crossing model agree well with the measurements. © 2012 IEEE.
Hossain N, Hild K, Jin SR, Yu SQ, Johnson SR, Ding D, Zhang YH, Sweeney SJ (2013) The influence of growth conditions on carrier recombination mechanisms in 1.3 ¼m GaAsSb/GaAs quantum well lasers, Applied Physics Letters 102 (4)
We investigate the temperature and pressure dependence of the threshold current density of edge-emitting GaAsSb/GaAs quantum well (QW) lasers with different device characteristics. Thermally activated carrier leakage via defects is found to be very sensitive to the growth conditions of GaAsSb QWs. An optimization of the growth conditions reduces the nonradiative recombination mechanisms from 93% to 76% at room temperature. This improvement in carrier recombination mechanisms leads to a large improvement in the threshold current density from 533 Acm-2/QW to 138 Acm-2/QW and the characteristic temperature, T0 (T1), from 51 ± 5 K (104 ± 16 K) to 62 ± 2 K (138 ± 7 K) near room temperature. © 2013 American Institute of Physics.
Sweeney SJ, Marko IP, Jin SR, Hild K, Batool Z, Ludewig P, Natterman L, Bushell Z, Stolz W, Volz K, Broderick CA, Usman M, Harnedy PE, O'Reilly EP, Butkute R, Pacebutas V, Geizutis A, Krotkus A (2014) Electrically injected GaAsBi Quantum Well Lasers, 2014 24TH IEEE INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE (ISLC 2014) pp. 80-81 IEEE COMPUTER SOC
Hild K, Sweeney SJ, Wright S, Lock DA, Jin SR, Marko IP, Johnson SR, Chaparro SA, Yu S-Q, Zhang Y-H (2006) Carrier recombination in 1.3 mu m GaAsSb/GaAs quantum well lasers, APPLIED PHYSICS LETTERS 89 (17) ARTN 173509 AMER INST PHYSICS
Ludewig P, Knaub N, Hossain N, Reinhard S, Nattermann L, Marko IP, Jin SR, Hild K, Chatterjee S, Stolz W, Sweeney SJ, Volz K (2013) Electrical injection Ga(AsBi)/(AlGa)As single quantum well laser, Applied Physics Letters 102 (24)
The Ga(AsBi) material system opens opportunities in the field of high efficiency infrared laser diodes. We report on the growth, structural investigations, and lasing properties of dilute bismide Ga(AsBi)/(AlGa)As single quantum well lasers with 2.2% Bi grown by metal organic vapor phase epitaxy on GaAs (001) substrates. Electrically injected laser operation at room temperature is achieved with a threshold current density of 1.56 kA/cm2 at an emission wavelength of
Hosea TJC, Cripps SA, Sale TE, Hild K (2006) Analysis of reflectance and modulation spectroscopic lineshapes in optoelectronic device structures, APPLIED SURFACE SCIENCE 253 (1) pp. 70-79 ELSEVIER SCIENCE BV
Broderick CA, Jin S, Marko Igor, Hild Konstanze, Ludewig P, Bushell Zoe, Stolz W, Rorison JM, O?Reilly EP, Volz K, Sweeney Stephen (2017) GaAs1?xBix/GaNyAs1?y type-II quantum wells: novel strain-balanced heterostructures for GaAs-based near- and mid-infrared photonics, Scientific Reports 7 46371 Nature Publishing Group
The potential to extend the emission wavelength of photonic devices further into the near- and midinfrared via pseudomorphic growth on conventional GaAs substrates is appealing for a number of communications and sensing applications. We present a new class of GaAs-based quantum well (QW) heterostructure that exploits the unusual impact of Bi and N on the GaAs band structure to produce type-II QWs having long emission wavelengths with little or no net strain relative to GaAs, while also providing control over important laser loss processes. We theoretically and experimentally demonstrate the potential of GaAs1?xBix/GaNyAs1?y type-II QWs on GaAs and show that this approach offers optical emission and absorption at wavelengths up to ~3 ¼m utilising strain-balanced structures, a first for GaAs-based QWs. Experimental measurements on a prototype GaAs0.967Bi0.033/GaN0.062As0.938 structure, grown via metal-organic vapour phase epitaxy, indicate good structural quality and exhibit both photoluminescence and absorption at room temperature. The measured photoluminescence peak wavelength of 1.72 ¼m is in good agreement with theoretical calculations and is one of the longest emission wavelengths achieved on GaAs to date using a pseudomorphically grown heterostructure. These results demonstrate the significant potential of this new class of III-V heterostructure for longwavelength applications.
Hild K, Sweeney S, Lock D, Wright S, Wang J, Johnson S, Zhang Y (2005) On the thermal stability of 1.3 mu m GaAsSb/GaAs-based lasers, 2005 IEEE LEOS Annual Meeting Conference Proceedings (LEOS) pp. 330-331 IEEE
In spite of the almost ideal variation of the radiative current of 1.3 mu m GaAsSb/GaAs-based lasers, the threshold current, J(th), is high due to non-radiative recombination accounting for 90% J(th) near room temperature. This also gives rise to low T-0 values similar to 60K close to room temperature, similar to that for InGaAsP/InP.
Bonmati-Carrion María Ángeles, Hild Konstanze, Isherwood Cheryl, Sweeney Stephen J, Revell Victoria, Madrid Juan Antonio, Rol María Ángeles, Skene Debra (2018) Effect of single and combined monochromatic light on the human pupillary light response, Frontiers in Neurology 9 1019 Frontiers Media
The pupillary light reflex (PLR) is a neurological reflex driven by rods, cones, and melanopsin-containing retinal ganglion cells. Our aim was to achieve a more precise picture of the effects of 5-min duration monochromatic light stimuli, alone or in combination, on the human PLR, to determine its spectral sensitivity and to assess the importance of photon flux. Using pupillometry, the PLR was assessed in 13 participants (6 women) aged 27.2 ± 5.41 years (mean ± SD) during 5-min light stimuli of purple (437 nm), blue (479 nm), red (627 nm), and combinations of red+purple or red+blue light. In addition, nine 5-min, photon-matched light stimuli, ranging in 10 nm increments peaking between 420 and 500 nm were tested in 15 participants (8 women) aged 25.7 ± 8.90 years. Maximum pupil constriction, time to achieve this, constriction velocity, area under the curve (AUC) at short (0?60 s), and longer duration (240?300 s) light exposures, and 6-s post-illumination pupillary response (6-s PIPR) were assessed. Photoreceptor activation was estimated by mathematical modeling. The velocity of constriction was significantly faster with blue monochromatic light than with red or purple light. Within the blue light spectrum (between 420 and 500 nm), the velocity of constriction was significantly faster with the 480 nm light stimulus, while the slowest pupil constriction was observed with 430 nm light. Maximum pupil constriction was achieved with 470 nm light, and the greatest AUC0?60 and AUC240?300 was observed with 490 and 460 nm light, respectively. The 6-s PIPR was maximum after 490 nm light stimulus. Both the transient (AUC0?60) and sustained (AUC240?300) response was significantly correlated with melanopic activation. Higher photon fluxes for both purple and blue light produced greater amplitude sustained pupillary constriction. The findings confirm human PLR dependence on wavelength, monochromatic or bichromatic light and photon flux under 5-min duration light stimuli. Since the most rapid and high amplitude PLR occurred within the 460?490 nm light range (alone or combined), our results suggest that color discrimination should be studied under total or partial substitution of this blue light range (460?490 nm) by shorter wavelengths (~440 nm). Thus for nocturnal lighting, replacement of blue light with purple light might be a plausible solution to preserve color discrimination while minimizing melanopic activation.