| 1. |
- Aggerstam, Thomas, et al.
(author)
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AlGaN/GaN high-electron-mobility transistors on sapphire with Fe-doped GaN buffer layer by MOVPE
- 2006
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In: Physica Status Solidi C - Current Topics in Solid State Physics. - : Wiley. ; , s. 2373-2376
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Conference paper (peer-reviewed)abstract
- A simple AlGaN/GaN HEMT structure without any interlayer on Fe-doped GaN (GaN:Fe) grown by LP-MOVPE in one single run on sapphire is demonstrated. The surface segregation of Fe in GaN occurring during growth is identified. Hall measurements yield 2DEG (two dimensional electron gas) mobilities of 1700 and 10700 cm2/Vs and sheet carrier concentrations of 5.1×10 12 and 5.7×1012 cm-2 at 300 K and 20 K, respectively. Good pinch-off current-voltage (ID-VD) characteristics is observed from AlGaN/GaN HEMTs. A maximum drain current density of 0.6 A/mm and a peak extrinsic transconductance of 200 mS/mm have been observed. The HEMT structure yields very good device isolation as indicated by an isolation current of ≀1 nA at 20 V.
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| 2. |
- Aggerstam, Thomas, et al.
(author)
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Electron and hole capture cross-sections of Fe acceptors in GaN:Fe epitaxially grown on sapphire
- 2007
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In: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 36:12, s. 1621-1624
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Journal article (peer-reviewed)abstract
- Carrier trapping of Fe (3+)/Fe2+ deep acceptors in epitaxially grown GaN:Fe on sapphire was studied by time-resolved photoluminescence. For the investigated Fe doping levels on the order of 10(18) cm(-3), the luminescence decay times are strongly dependent on the Fe concentration, indicating that Fe centers act as predominant nonradiative recombination channels. Linear dependence of the decay time on the iron concentration allows estimation of the electron capture cross-section for the Fe3+ ions, which is equal to 1.9 x 10(-15) cm(2). The upper bound for the cross-section of the hole capture of Fe2+ was evaluated as 10 x 10(-15) cm
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| 3. |
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| 4. |
- Aggerstam, Thomas, et al.
(author)
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GaN/AlN multiple quantum well structures grown by MBE on GaN templates for 1.55 mu m intersubband absorption
- 2007
-
In: Quantum Sensing and Nanophotonic Devices IV. - : SPIE. - 9780819465924 ; 6479, s. 64791E-
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Conference paper (peer-reviewed)abstract
- We have used MBE to grow MQW structures on MOVPE GaN/sapphire templates. The MQW devices are intended for high speed intersubband electroabsorption modulator devices operating at 1.55-mu m. The GaN/AlN multiple quantum well material was systematically studied regarding the surface morphology, structural characterization and optical property by atomic force microscopy, X-ray diffraction and Fourier transform infrared spectroscopy, respectively. The intersubband resonance energy was also calculated considering many-body effects in n-type doped structures. The multiple quantum well structure showed superior performance in terms of linewidth when grown on GaN templates as compared on sapphire. GaN quantum well and AlN barriers with a thickness of 3.3 and 4.2 nm respectively resulted in FWHM of the intersubband absorption peak as low as 93 meV at an absorption energy of 700 meV. This is promising for intersubband modulator applications.
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| 5. |
- Aggerstam, Thomas, et al.
(author)
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Investigation of the interface properties of MOVPE grown AlGaN/GaN high electron mobility transistor (HEMT) structures on sapphire
- 2006
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:2, s. 705-707
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Journal article (peer-reviewed)abstract
- We have developed a virtual GaN substrate on sapphire based on a two-step growth method. By optimizing the growth scheme for the virtual substrate we have improved crystal quality and reduced interface roughness. Our Al0.22Ga0.78N/GaN HEMT structure grown on the optimized semi-insulating GaN virtual substrate, exhibits Hall mobilities as high as 1720 and 7350 cm(2)/Vs and sheet carrier concentrations of 8.4 x 1012 and 10.0 x 1012 cm(-2) at 300 K and 20 K, respectively The presence of good AlGaN/GaN interface quality and surface morphology is also substantiated by X-Ray reflectivity and Atomic Force Microscopy measurements. A simplified transport model is used to fit the experimental Hall mobility.
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| 6. |
- Aggerstam, Thomas, et al.
(author)
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Selectively oxidized vertical-cavity surface-emitting lasers for high-speed data communication
- 2001
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In: Proc. SPIE 4286, SPIE's Optoelectronics 2001, Photonics West, San Jose, US. - Bellingham, WA, ETATS-UNIS : Society of Photo-Optical Instrumentation Engineers. ; , s. 96-
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Conference paper (peer-reviewed)abstract
- MITEL Semiconductor is developing the next generation low cost, high performance transceivers for data communication. The increasing quantity of data being transferred over the Internet demands very high capacity interconnects. A low cost, high-performance alternative is the use of parallel fiber interconnects where the light is, for example, coupled into a 12-channel fiber-ribbon. Parallel interconnects require good uniformity in order to reduce escalating costs and complexity. In this paper we report on the static and the modulation properties of 850nm multimode oxide VCSELs for use in such Gb/s transceiver system. Static power-current-voltage characteristics with good uniformity were obtained for different structures, with threshold currents down to sub-mA. A maximum small signal 3-dB bandwidth of 10 GHz and a modulation current efficiency up to 8.4 GHz/√[mA] were measured. Single channel results are presented for VCSELs operated at data rates from 2.5-10Gb/s.
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| 7. |
- Andersson, Thorvald, 1946, et al.
(author)
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Macroscopic defects in GaN/AlN multiple quantum well structures grown by MBE on GaN templates
- 2009
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In: Microelectronics Journal. - : Elsevier BV. - 0026-2692. ; 40:2, s. 360-362
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Journal article (peer-reviewed)abstract
- We have used MBE to grow in AlN/GaN superlattices, with different number of periods, on 2.5-mu m-thick MOVPE-GaN templates to study the development of defects such as surface deformation due to strain. After growth the samples were studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), XRD and Fourier transform infrared spectroscopy (FT-IR). The strain increased with the number of quantum wells (QWs) and eventually caused defects such as microcracks visible by optical microscopy at four or more QW periods. High-resolution TEM images showed shallow recessions on the surface (surface deformation) indicating formation of microcracks in the MQW region. The measured intersubband (IS) absorption linewidth from a four period structure was 97 meV, which is comparable with the spectrum from a 10 period structure at an absorption energy of similar to 700 meV. This indicates that the interface quality of the MQW is not substantially affected by the presence of cracks.
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| 8. |
- Azarov, A.Yu., et al.
(author)
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High dose Fe implantation of gan : Damage build-up and dopant redistribution
- 2008
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In: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY. - : IOP Publishing. ; 100:4, s. 042036-
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Conference paper (peer-reviewed)abstract
- Undoped GaN epilayers implanted at room temperature with 50-325 keV Fe + ions in the fluence range of 1015 - 1017 ions/cm are studied by a combination of Rutherford backscattering/channeling spectrometry and time-of-flight elastic recoil detection analysis. Results show that for high ion fluences (>1 × 1016 cm-2) enhanced Fe concentration closer to the surface is observed. The Fe redistribution towards the surface increases as the ion fluence increases. Our findings are attributed to radiation enhanced diffusion during ion implantation and increasing of Fe diffusivity in the implantation-induced amorphous phase near the surface.
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| 9. |
- Gautier, S., et al.
(author)
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AlGaN/AlN multiple quantum wells grown by MOVPE on AlN templates using nitrogen as a carrier gas
- 2008
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 310:23, s. 4927-4931
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Journal article (peer-reviewed)abstract
- AlxGa1-xN/AlN multiple quantum wells (MQWs) structures were grown by metalorganic vapour phase epitaxy (MOVPE) on pseudo AlN substrates using nitrogen as a carrier gas. Results of X-ray diffraction (XRD) and reciprocal space mapping (RSM) indicated no sign of strain relaxation in the quantum wells with respect to the AlN substrate. The MQW parameters such as thicknesses, growth rates and material compositions were extracted from XRD measurements and demonstrated an agreement with our growth conditions. No indication of parasitic reactions between ammonia and trimethyl-aluminium (TMAI) was detected in our growth process. Optical measurements revealed well-defined photoluminescence peaks at 288 and 280 nm, which are in a good agreement with the transmission experimental data. The piezoelectric field value in the Studied structures was estimated to be 900kV/cm.
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| 10. |
- Holmström, Petter, et al.
(author)
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Intersubband photonic devices by group-III nitrides
- 2007
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In: Optoelectronic Materials And Devices II. - : SPIE. - 9780819469458 ; , s. N7821-N7821
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Conference paper (peer-reviewed)abstract
- The characteristics of intersubband transitions in III-nitride quantum wells are promising for detectors and all-optical switches through a high intrinsic speed (similar to 1 THz), and can also provide a high optical saturation power and a desired small negative chirp parameter in electroabsorption modulators. The high LO-phonon energy allows to improve the operating temperature of THz emitters. Recent achievements and prospects for intersubband III-nitride photonic devices, mainly for lambda=1.55 mu m, are briefly reviewed. Further, means to enhance material quality by achieving crack-free growth of GaN/AlN multiple-quantum-well (MQW) structures, and by employing intersubband transitions in multiple-quantum-disk (MQD) structures incorporated into dislocation free GaN nanocolumns are discussed. We investigate the occurrence of cracks in MBE-grown GaN/AlN MQWs on GaN MOVPE templates with respect to the buffer layer, the number of QWs and the temperature reduction rate after growth. Intersubband absorption in GaN/AlN MQDs in the wavelength range 1.38-1.72 mu m is demonstrated in three samples grown on Si(111).
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| 11. |
- Liu, Xinju, 1979, et al.
(author)
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Cracks in GaN/AlN multiple quantum well structures grown by MBE
- 2008
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In: Journal of Physics, Conference Series. - : Institute of Physics (IOP). - 1742-6588 .- 1742-6596. ; 100, s. 042026-
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Journal article (peer-reviewed)abstract
- Due to the large lattice constant mismatch and thermal expansion coefficient difference between GaN and AlN, large strain is generated inside the GaN/AlN multiple quantum wells, which causes cracks in the structure. We investigated such cracks by optical microscopy and AFM. The crack density was studied with buffer and cap layer thickness, the number of quantum well periods, and the temperature reduction rate after growth as parameters. It was found that the crack density increased exponentially, with the number of periods above 4. Besides, a very thin, 100 nm, GaN buffer layer and similar to 300 nm GaN cap layer greatly reduced the crack density.
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| 12. |
- Liu, Xinju, 1979, et al.
(author)
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Growth of GaN and GaN/AlN multiple quantum wells on sapphire, Si and GaN template by molecular beam epiotaxy
- 2007
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 300:1, s. 79-82
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Journal article (peer-reviewed)abstract
- GaN layers of 280 nm thick were grown on sapphire, silicon (1 1 1) and GaN template by plasma assisted molecular beam epitaxy. From atomic force microscopy and high-resolution X-ray diffraction, it was found that GaN grown on sapphire and template gave smooth surface (RMS less then 0.5 nm) and very high crystalline quality (FWHM of (0 0 0 2) scan on sapphire only 48 arcsec). However, GaN growth on Si (1 1 1) provided rough surface and poor crystalline quality. The GaN/AlN multiple quantum well structures were grown on sapphire and template. Intersubband absorption spectra from Fourier transform infrared spectroscopy indicated that layers on GaN templates had better performances than on sapphire substrates.
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| 13. |
- Liu, Xinju, 1979, et al.
(author)
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Investigation of intersubband absorption of GaN/AlN multiple quantum wells grown on different substrates by molecular beam epitaxy
- 2007
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 301:SPEC. ISS., s. 301-302
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Journal article (peer-reviewed)abstract
- Ten period GaN/AlN multiple quantum well (MQW) structures were grown by plasma-assisted molecular beam epitaxy (MBE) on sapphire substrates and metal-organic vapour-phase epitaxy (MOVPE)-grown GaN templates. Samples were investigated by high-resolution X-ray diffraction (HR-XRD) and Fourier transform infrared (FT-IR) spectroscopy. Intersubband (IS) absorbances and FWHM of IS absorption peaks indicated that samples grown on the GaN templates had better characteristics, resulting in a FWHM as low as 93 meV at a peak energy of 700 meV.
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| 14. |
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| 15. |
- Lo, Ikai, et al.
(author)
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Study of two-subband population in Fe-doped AlxGa1-xN/GaN heterostructures by persistent photoconductivity effect
- 2006
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:24, s. 245325-
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Journal article (peer-reviewed)abstract
- The electronic properties of Fe-doped Al0.31Ga0.69N/GaN heterostructures have been studied by Shubnikov-de Haas measurement. The lowest two subbands of the two-dimensional electron gas in the heterointerface were populated. After the low temperature illumination, the electron density increases from 11.99x10(12) cm(-2) to 13.40x10(12) cm(-2) for the first subband and from 0.66x10(12) cm(-2) to 0.94x10(12) cm(-2) for the second subband. The persistent photoconductivity effect (similar to 13% increase) is mostly attributed to the Fe-related deep-donor level in GaN layer. The second subband starts to populate when the first subband is filled at a density of 9.40x10(12) cm(-2). We obtained the energy separation between the first and second subbands to be 105 meV.
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| 16. |
- Ougazzaden, A., et al.
(author)
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GaN thin films on z- and x-cut LiNbO3 substrates by MOVPE
- 2008
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In: PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS. - : Wiley. ; , s. 1565-1567
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Conference paper (peer-reviewed)abstract
- We report epitaxial growth of GaN layers on z- and x-cut LiNbO3 substrates using MOVPE. GaN layers with the thickness of 450 nm were characterized using X-ray diffraction. For both, z- and x-cut orientations of LiNbO3 substrates, the GaN layers have c-axis orientation normal to the substrate plane and the in-plane lattice orientation of GaN layers coincides with the primary axes of LiNbO3 substrates. Although GaN layers exhibit almost complete strain relaxation, the residual compressive strain determined with respect to a freestanding GaN is of the order of +0.37% and +0.2% for z- and x-cut substrates, respectively.
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| 17. |
- Ougazzaden, A., et al.
(author)
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Growth of GaN by metal organic vapor phase epitaxy on ZnO-buffered c-sapphire substrates
- 2008
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 310:5, s. 944-947
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Journal article (peer-reviewed)abstract
- The materials quality and availability of large-area bulk GaN substrates is currently considered a key problem for the continuing development of improved GaN-based devices. Since industrial fabrication of bulk GaN substrates with suitable materials quality has proven very difficult, the opto-GaN industry is currently based on heteroepitaxy using either c-sapphire or 6H SiC substrates. ZnO is promising as a substrate material for GaN because it has the same wurtzite structure and a relatively small lattice mismatch (similar to 1.8%). In this study, we have successfully grown GaN by MOVPE on ZnO-buffered c-sapphire. The growth conditions required to both prevent ZnO degradation and grow monocrystal thin film of GaN have been obtained. SEM, HRXRD and micro-Raman characterizations underlined the presence of the two layers GaN and ZnO with high structural quality.
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| 18. |
- Ougazzaden, A., et al.
(author)
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Progress on new wide bandgap materials BGaN, BGaAlN and their potential applications
- 2007
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In: Quantum Sensing and Nanophotonic Devices IV. - : SPIE. - 9780819465924 ; , s. G4791-G4791
-
Conference paper (peer-reviewed)abstract
- The development of wide band gap semiconductors extends their applications in optoelectronics devices to the UV domain. Compact lasers and high sensitivity APD detectors in UV range are currently needed for different applications such as, purification, covert communication and real time detection of airborne pathogens. Until now, the full exploitation of these potential materials has been limited by the lack of suitable GaN substrates. Recently, a novel class of materials has been reported based on BGaN and BAlN, potentially reducing the crystal defect densities by orders of magnitude compared to existing wide band gap heterostructures. Characteristics of these new alloys are similar to those of AlGaN materials with the advantage that these can be lattice matched to AlN and SiC substrates. In addition, these materials offer the possibility of using quaternary BAlGaN alloys at Ultra Violet (UV) wavelengths and hence lead to more degrees of freedom in designing sophisticated device structures. In this paper we describe the MOVPE growth conditions used to incorporate boron in GaN and AlGaN. Detailed characterization and analysis in terms of structural and electrical properties are discussed.
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| 19. |
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| 20. |
- Usman, Muhammad, et al.
(author)
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Electrical and structural characterization of ion implanted GaN
- 2009
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 267:8-9, s. 1561-1563
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Journal article (peer-reviewed)abstract
- Ion implantation induced defects and their consequent electrical impact have been investigated. Unintentionally doped n-type gallium nitride was implanted with 100 keV Si+ and 300 keV Ar+ ions in a fluence range of 10(14)-10(15) ions/cm(2). The samples were characterized with Rutherford backscattering/Channeling method for damage buildup. Time of flight elastic recoil detection analysis was implied on the Si implanted samples to see the ion depth distribution. At implanted GaN samples were studied electrically with scanning spreading resistance microscopy. Our results show that an At fluence of 5 x 10(14) cm(-2) increases the resistance by five orders of magnitude to a maximum value. For the highest fluence, 6 x 10(15) cm(-2), the resistivity decreases by two orders of magnitude.
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