randihaa

• Storebø, Asta Katrine; Brudevoll, Trond; Selvig, Espen; Hansen, Runar Wattum; Lorentzen, Torgeir & Haakenaasen, Randi (2022). Effect of the Series Resistance on the Current Response of a HgCdTe Avalanche Photodiode Under High-intensity Nanosecond Irradiation. Journal of Electronic Materials. ISSN 0361-5235. doi: 10.1007/s11664-022-09670-z. Full text in Research Archive Show summary

  We investigate the nonlinear signal current response of a Hg0.72Cd0.28Te avalanche photodiode (APD) irradiated by high-intensity, finite-duration laser pulses. At high irradiation levels and/or high gains, carrier-induced perturbations in the junction electric field and avalanche gain strongly influence the temporal behavior of the APD current. The total series resistance will play a major role here, and four values of the series resistance were used for mapping out the APD response. When striving for maximum achievable bandwidth, the internal junction capacitance and the internal series resistance set the ultimate limits for an APD. A signal analysis of these high-intensity nonlinear gain effects should therefore begin with an intrinsic APD, and proceed with adding appropriate external series resistances. A simultaneous modeling of the entire external circuit is then required. To this end, we have combined full-band Monte Carlo (MC) transport simulation in the active multiplication zone with conventional circuit modeling outside. We demonstrate how overshoot/undershoot and rapid oscillations in the signal current evolve in time as a function of the chosen external series resistances at two different high-intensity irradiation levels. Oscillations are shown to persist slightly beyond the duration of the laser pulse when operating the diode within the junction transit time-limited regime. The periodicity of the oscillations is related to the junction transit time and remains only weakly dependent on irradiation levels and external resistance values until we enter the resistance–capacitance (RC)-limited case. Here, a change occurs where oscillations are smoothed out as external series resistances are increased further.

• Haakenaasen, Randi; Selvig, Espen; Heier, Anne Cathrine; Lorentzen, Torgeir & Trosdahl-Iversen, Laila (2019). Improved Passivation Effect Due to Controlled Smoothing of the CdTe-HgCdTe Interface Gradient by Thermal Annealing. Journal of Electronic Materials. ISSN 0361-5235. doi: 10.1007/s11664-019-07415-z. Full text in Research Archive Show summary

  HgCdTe films grown by liquid phase epitaxy were passivated with CdTe grown by molecular beam epitaxy. A series of annealing tests with different temperatures and durations were then carried out in order to reach a two-fold goal: to smooth the gradients in Hg and Cd content across the HgCdTe film-passivation interface, and to create a Hg vacancy concentration of ∼ 1–2 × 1016 cm−3. We want the composition gradient to prevent minority carrier electrons from reaching the actual interface, as this may contain recombination centers that trap the electrons. Four different temperature–time combinations were tried for the first part of the annealing procedure (the smoothing of gradients), while they were all followed by a Hg vacancy procedure of 250°C for 18–24 h. Then some samples were cleaved, and energy-dispersive x-ray spectroscopy (EDS) line profiles were recorded on the cross sections to monitor the composition gradients. We could clearly see differences between the profiles from samples with the higher-temperature annealing, the lower-temperature annealing and no annealing. Secondary ion mass spectroscopy profiles on two samples verified the EDS results. On another subset of similar samples, planar diodes were processed and resistance-area (RA) values determined. The current–voltage (I–V) curves from the high-temperature annealed samples seemed dominated by leakage current and did generally not display diode characteristics. This could be explained by their EDS profiles, which showed a lot of Hg in the entire passivation layer. The EDS profiles from the three low-temperature annealing procedures were very similar, but planar diode I–V curves revealed diodes of varying quality, and their RA values were used to differentiate among them. The optimal annealing procedure was 300°C for 4 h, followed by 250°C for 24 h.

• Haakenaasen, Randi; Lauten, Oda; Selvig, Espen; Kongshaug, Kjell Ove; Røer, Eivind Jülke & Hansen, Runar Wattum (2019). Characterization of (111)B and (211)B CdZnTe Substrates for HgCdTe Growth. Journal of Electronic Materials. ISSN 0361-5235. 48(10). doi: 10.1007/s11664-019-07349-6. Full text in Research Archive Show summary

  We have studied state-of-the-art CdZnTe (211)B and (111)B substrates and compared them to each other and to substrates from an alternative vendor. The CdZnTe surface has been characterized both as-received and after growth preparation procedures using dark field optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, Fourier transform infrared transmission spectroscopy, and secondary ion mass spectroscopy. From these measurements we have obtained densities of particles and morphological defects with size > 0.5 μm, densities of small particles/features with size ≤ 100 nm, and substrate/film interface impurities. The state-of-the-art substrates all have remains of silica grit polishing particles around the edges. The as-received (111)B substrates had very few particles or morphological defects on the surface, but a Br:methanol surface preparation etch exposed a large number of features with sizes ≤ 100 nm. Some of these were silica grit particles, but most of them were Te precipitates. The (111)B substrate from an alternative vendor had a lot of different particles, stains, and voids. It improved significantly after a fine-polishing procedure, but still had the surface with most defects after surface preparation. The state-of-the-art (211)B had the largest as-received density of small features, but after Br:methanol etching this density (of Te precipitates and silica grit particles) was the same as for the etched (111)B substrate. SIMS measurements showed that some of the polishing grit particles ended up on the top surface after surface preparation. Hydrofluoric acid can be used to etch away the silica particles.

• Selvig, Espen; Kongshaug, Kjell Ove; Haakenaasen, Randi; Lorentzen, Torgeir & Brudevoll, Trond (2019). Descending Infrared Transmission Spectra of CdZnTe Substrates Due to Surface Roughness. Journal of Electronic Materials. ISSN 0361-5235. doi: 10.1007/s11664-019-07339-8. Full text in Research Archive Show summary

  (111)B-oriented Cd0.96Zn0.04Te substrates with rough surfaces have been found to have infrared (IR) transmission spectra which decrease rapidly in intensity as the photon energy increases. The rough surfaces were produced by Everson etching or rough polishing. The descending spectra could be qualitatively described by an equation found in the literature. Flat low intensity IR transmission spectra were found to be due to a combination of free carrier absorption and rough surfaces. The B-side of the substrate is the growth side. By etching the A-side of the substrate only we found that the black layer formed by the Everson etch on this side introduces two features in the IR transmission spectra: a dip at approx. 625 cm-1 and a special kind of ascending IR transmission spectrum: The ascending spectrum increases from approx. 65% at 500 cm-1 up to 72.5% at the highest wavenumbers around 4000 cm-1. There is a correlation between the dip and the ascending spectrum: Six out of the seven spectra with largest dip have the highest transmission at 4000 cm-1 suggesting a common origin.

• Tonheim, Celin Russøy; Sudbø, Aasmund Sveinung; Selvig, Espen & Haakenaasen, Randi (2011). Enhancement in Light Emission From Hg-Cd-Te Due to Surface Patterning. IEEE Photonics Technology Letters. ISSN 1041-1135. doi: 10.1109/LPT.2010.2090517. Full text in Research Archive Show summary

  Enhancement of light emission from HgCdTe due to surface patterning has been studied by means of photoluminescence (PL) spectroscopy. A triangular pattern of circular holes was etched into the CdTe layer grown on top of HgCdTe thin-film and multiple quantum well samples. Two different pattern lattice constants were used, giving lattice constant aG to emission wavelength ratios of 0.9, 1.2, and 2.1. The surface pattern was found to give 26%-35% enhancement in measured PL intensity.

• Foss, Steinar; Taftø, Johan & Haakenaasen, Randi (2010). A specimen preparation technique for plane-view studies of surfaces using transmission electron microscopy. Journal of Electron Microscopy. ISSN 0022-0744. 59(1), p. 27–31. doi: 10.1093/jmicro/dfp044. Full text in Research Archive Show summary

  A method for preparing plane-view transmission electron microscope (TEM) samples is presented. With this inclined pseudo-plane-view technique, the undisturbed surface of the sample can be studied in plane view. Thus, nanostructures on the surface of a substrate can be studied with TEM in much the same way as with scanning electron microscopy (SEM), but in transmission at a much higher spatial resolution and with the opportunity of performing nanoscale diffraction. A glued sandwich with two surfaces facing each other was thinned at a low angle relative to the surfaces. The resultant construction contained thin wedges of the surfaces upon which it was possible to do TEM analysis. SEM analysis before and TEM analysis after such sample preparation was found to be consistent.

• Haakenaasen, Randi; Selvig, Espen; Tonheim, Celin Russøy; Kongshaug, Kjell Ove; Lorentzen, Torgeir & Trosdahl-Iversen, Laila [Show all 8 contributors for this article] (2010). HgCdTe Research at FFI: Molecular Beam Epitaxy Growth and Characterization. Journal of Electronic Materials. ISSN 0361-5235. 39(7), p. 893–902. doi: 10.1007/s11664-010-1211-7. Full text in Research Archive Show summary

  This paper presents results from recent work on molecular beam epitaxy growth of HgCdTe at the Norwegian Defence Research Establishment (FFI), including studies of material properties and fabrication of photodiodes and nanostructures. Systematic studies of defect morphology in HgTe and Hg1−x Cd x Te have revealed that there is a minimum in the area covered by defects just below the onset of Te precipitation. The shape and density of microvoids in HgTe can be used to determine the deviation from the optimal growth temperature. This can be further related to the optimal growth temperature of Hg1−x Cd x Te with any Cd mole fraction by thermodynamic calculations. A mechanism for the formation of microvoids and needles has been presented. Photoluminescence (PL) has been used to study layers without doping and with Hg vacancy, Ag, and In doping. Planar photodiodes with high dynamic resistance and good quantum efficiency were fabricated by ion-milling vacancy-doped mid-wave and long-wave infrared layers. Quantum wells (QWs) with good crystallinity and high PL light output have been grown. Surface patterning has been found to enhance light emission from HgCdTe thin-film and QW samples by ∼30%. Single-crystal HgTe and segmented HgTe/Te nanowires have been grown, and the resistivity of the nanowires has been measured by conductive atomic force microscopy (AFM), where the AFM tip has been used as a mobile electrode.

• Haakenaasen, Randi & Selvig, Espen (2010). Molecular Beam Epitaxy Growth of Nanowires in the Hg1-xCdxTe Material System. In Prete, Paola (Eds.), Nanowires. IntechOpen. ISSN 9789537619794. p. 79–96. Full text in Research Archive
• Gundersen, Paul; Kongshaug, Kjell Ove; Selvig, Espen & Haakenaasen, Randi (2010). Electrical characterization of HgTe nanowires using conductive atomic force microscopy. Journal of Applied Physics. ISSN 0021-8979. 108(11). doi: 10.1063/1.3512960. Full text in Research Archive Show summary

  Self-organized HgTe nanowires grown by molecular beam epitaxy (MBE) have been characterized using conductive atomic force microscopy. As HgTe will degrade or evaporate at normal baking temperatures for electron beam lithography (EBL) resists, an alternative method was developed. Using low temperature optical lithography processes, large Au contacts were deposited on a sample covered with randomly oriented, lateral HgTe nanowires. Nanowires partly covered by the large electrodes were identified with a scanning electron microscope and then localized in the atomic force microscope (AFM). The conductive tip of the AFM was then used as a movable electrode to measure current-voltage curves at several locations on HgTe nanowires. The measurements revealed that polycrystalline nanowires had diffusive electron transport, with resistivities two orders of magnitude larger than that of an MBE-grown HgTe film. The difference can be explained by scattering at the rough surface walls and at the grain boundaries in the wires. The method can be a solution when EBL is not available or requires too high temperature, or when measurements at several positions along a wire are required.

• Haakenaasen, Randi; Selvig, Espen; Hadzialic, S; Skauli, Torbjørn; Hansen, Vidar & Tibballs, J.E. [Show all 12 contributors for this article] (2008). Nanowires in the CdHgTe material system. Journal of Electronic Materials. ISSN 0361-5235. 37(9), p. 1311–1317. Full text in Research Archive Show summary

  HgTe nanowires have been grown by molecular beam epitaxy (MBE). They are nucleated at Au particles on Si or GaAs substrates and subsequently self-organize and grow laterally on the surface into 20-50 nm wide, 0.5-1 mu m long twisted, but single-crystal, wires. Further growth gives longer, wider, and straighter polycrystalline wires. When unimpeded by Au particles on the surface, the wires become straight and consist of segments of cubic < 111 > HgTe and hexagonal < 001 > Te parallel to the wire. Te nanowires and Au nanowires have also occasionally been formed. All attempts to grow CdHgTe on Si substrates with or without Au particles have resulted in polycrystalline layers. The phase diagrams and diffusion coefficients imply that CdHgTe or HgTe nanowires will not grow by the vapor-liquid-solid technique at the low MBE growth temperatures. SiO2 functions as a mask for selective growth of HgTe, but not for CdHgTe.

• Breivik, Magnus; Selvig, Espen; Tonheim, Celin Russøy; Brendhagen, Erik; Brudevoll, Trond & Rheenen, Arthur D. van [Show all 10 contributors for this article] (2008). Photoluminescence from CdxHg1-xTe. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 100. doi: 10.1088/1742-6596/100/4/042041. Full text in Research Archive Show summary

  We present important aspects of photoluminescence (PL) of CdxHg1-xTe in the infrared part of the spectrum where background thermal radiation significantly affects the PL spectrum. We show how the background spectrum can be removed from the data. We also show how the wavelength of the excitation laser affects the relative intensity of the PL peaks from a multi-layer structure. Finally, we present temperature dependent PL of a Cd0.36Hg0.64Te/Cd0.61Hg0.39Te multiple quantum well structure grown on a 4 mu m thick Cd0.36Hg0.64Te buffer layer. We attribute the low temperature peak from the buffer layer to impurities. The impurity levels are depopulated as the temperature increases, resulting in a decreased PL peak intensity. Above similar to 200 K a band-to-band peak from the buffer layer is observed. The quantum well peak persists up to similar to 200 K.

• Selvig, Espen; Tonheim, Celin Russøy; Lorentzen, Torgeir; Kongshaug, Kjell Ove; Skauli, Torbjørn & Haakenaasen, Randi (2008). Defects in HgTe and CdHgTe grown by molecular beam epitaxy. Journal of Electronic Materials. ISSN 0361-5235. 37(9), p. 1444–1452. doi: 10.1007/s11664-008-0447-y. Full text in Research Archive Show summary

  The defect morphology in HgTe and CdHgTe was studied in (211)B-oriented layers grown in a 20 degrees C temperature range around the optimal growth temperature. The density of defects varies strongly with the growth temperature. In HgTe, the shape of the microvoid defects is very sensitive to the growth temperature and can be used to determine the deviation from the optimal growth temperature. Using thermodynamical modeling, the optimal growth temperature for CdHgTe can then be calculated. We describe a mechanism for the formation of microvoids and needles which involves preferential surface diffusion of Te combined with an impurity or defect on the substrate. Microvoids on (111)B-oriented partially twinned HgTe layers were also studied. The microvoids in the twinned parts of the layer were found to be rotated 180 deg relative to the untwinned parts of the layer.

• Selvig, Espen; Tonheim, Celin Russøy; Kongshaug, Kjell Ove; Skauli, Torbjørn; Hemmen, H & Lorentzen, Torgeir [Show all 7 contributors for this article] (2008). Defects in CdHgTe grown by molecular beam epitaxy on, (211)B-oriented CdZnTe substrates. Journal of Vacuum Science & Technology B. ISSN 1071-1023. 26(2), p. 525–533. doi: 10.1116/1.2868782. Full text in Research Archive
• Haakenaasen, Randi; Selvig, Espen; Foss, Steinar; Trosdahl-Iversen, Laila & Taftø, Johan (2008). Segmented nanowires of HgTe and Te grown by molecular beam epitaxy. Applied Physics Letters. ISSN 0003-6951. 92. doi: 10.1063/1.2898166. Full text in Research Archive Show summary

  Heterostructured nanowires consisting of alternating segments of HgTe and Te have been grown by molecular beam epitaxy. The cubic < 111 > HgTe and the hexagonal < 001 > Te directions are oriented along the wire. The 15-70 nm wide, 0.5-1.5 mu m long wires are nucleated at Au particles and grow laterally on Si substrates, but they are not epitaxially coupled to the substrates. An excess of Te relative to Hg during growth could explain the segmentation, as the bulk phase diagram then allows only HgTe and elemental Te. Alternating between these two phases is facilitated by the epitaxial match between the HgTe and Te segments. (C) 2008 American Institute of Physics.

• Tonheim, Celin Russøy; Selvig, Espen; Nicolas, Stephane; Gunnæs, A.E.; Breivik, Magnus & Haakenaasen, Randi (2008). Excitation density dependence of the photoluminescence from CdxHg1-xTe multiple quantum wells. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 100. doi: 10.1088/1742-6596/100/4/042024. Full text in Research Archive Show summary

  A study of the photoluminescence from a four-period CdxHg1-xTe multiple quantum well structure at 11 K as a function of excitation density is presented. High-resolution X-ray diffraction and transmission electron microscopy revealed that the quantum well structure is of high quality. This was supported by the narrow photoluminescence peak originating in the ground state electron - heavy hole transition, with a full width at half maximum of only 7.4 meV for an excitation density of 1.3 W/cm(2). When the excitation density was increased from 1.3 to 23.4 W/cm(2), the peak position was shifted toward higher energy by 2.6 meV and the full width at half maximum increased from 7.4 to 10.9 meV.

• Selvig, Espen; Tonheim, Celin Russøy; Kongshaug, Kjell Ove; Skauli, Torbjørn; Lorentzen, Torgeir & Haakenaasen, Randi (2007). Defects in HgTe grown by molecular beam epitaxy on (211)B-oriented CdZnTe substrates. Journal of Vacuum Science & Technology B. ISSN 1071-1023. 25(6), p. 1776–1784. doi: 10.1116/1.2787876. Full text in Research Archive
• Selvig, Espen; Hadzialic, S; Skauli, Torbjørn; Steen, Harald; Hansen, Vidar & Trosdahl-Iversen, L [Show all 9 contributors for this article] (2006). Growth of HgTe nanowires. Physica scripta. Topical Issues. ISSN 0281-1847. 126, p. 115–120. Full text in Research Archive
• Haakenaasen, Randi; Steen, Helge; Selvig, Espen; Rheenen, Arthur Dirk Van; Trosdahl-Iversen, Laila & Hall, D. [Show all 10 contributors for this article] (2006). Imaging photovoltaic infrared CdHgTe detectors. Physica Scripta. ISSN 0031-8949. T126, p. 31–36. doi: 10.1088/0031-8949/2006/T126/007. Full text in Research Archive
• Haakenaasen, Randi; Steen, Helge; Selvig, Espen; Lorentzen, Torgeir; Rheenen, Arthur Dirk Van & Trosdahl-Iversen, Laila [Show all 9 contributors for this article] (2005). Imaging One-Dimensional and Two-Dimensional Planar Photodiode Detectors Fabricated by Ion Milling Molecular Beam Epitaxy CdHgTe. Journal of Electronic Materials. ISSN 0361-5235. 34(6), p. 922–927. doi: 10.1007/s11664-005-0043-3. Full text in Research Archive

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• Haakenaasen, Randi; Lauten, Oda; Selvig, Espen; Kongshaug, Kjell Ove; Røer, Eivind Jülke & Hansen, Runar Wattum (2018). Characterization of (111)B and (211)B CdZnTe substrates. Full text in Research Archive
• Haakenaasen, Randi; Selvig, Espen; Heier, Anne Cathrine; Lorentzen, Torgeir & Trosdahl-Iversen, Laila (2018). Annealing procedure for vacancy doping HgCdTe under CdTe passivation. Full text in Research Archive
• Selvig, Espen; Kongshaug, Kjell Ove; Haakenaasen, Randi; Lorentzen, Torgeir & Brudevoll, Trond (2018). Descending infrared transmission spectra of CdZnTe substrates due to surface roughness. Full text in Research Archive Show summary

  (111)B-oriented Cd0.96Zn0.04Te substrates with rough surfaces have been found to have infrared (IR) transmission spectra which decrease rapidly in intensity as the photon energy increases. The rough surfaces were produced by Everson etching or rough polishing. The descending spectra could be qualitatively described by an equation found in the literature. Flat low intensity IR transmission spectra were found to be due to a combination of free carrier absorption and rough surfaces. By etching the A-side of the substrate only we found that the black layer formed by the Everson etch on this side introduces two new features in the IR transmission spectra: a dip at approx. 625 cm-1 and a special kind of ascending IR transmission spectrum: The ascending spectrum increases from approx. 65% at 500 cm-1 up to 72.5% at the highest wavenumbers around 4000 cm-1. There is a correlation between the dip and this new ascending spectrum: Six out of the seven spectra with largest dip have the highest transmission at 4000 cm-1 suggesting a common origin.

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