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  • 1
    Electronic Resource
    Electronic Resource
    Metalorganic chemical vapor deposition of high mobility AlGaN/GaN heterostructures (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5850-5857 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article, we discuss parameters influencing (a) the properties of thin AlxGa1−xN layers grown by metalorganic chemical vapor deposition and (b) the electrical properties of the two-dimensional electron gas (2DEG) forming at the AlxGa1−xN/GaN heterojunction. For xAl〉0.3, the AlxGa1−xN layers showed a strong tendency towards defect formation and transition into an island growth mode. Atomically smooth, coherently strained AlxGa1−xN layers were obtained under conditions that ensured a high surface mobility of adsorbed metal species during growth. The electron mobility of the 2DEG formed at the AlxGa1−xN/GaN interface strongly decreased with increasing aluminum mole fraction in the AlxGa1−xN layer and increasing interface roughness, as evaluated by atomic force microscopy of the surfaces prior to AlxGa1−xN deposition. In the case of modulation doped structures (GaN/AlxGa1−xN/AlxGa1−xN:Si/AlxGa1−xN), the electron mobility decreased with decreasing thickness of the undoped spacer layer and increasing silicon doping. The electron mobility was only moderately affected by the dislocation density in the films and independent of the growth temperature of the AlxGa1−xN layers at xAl=0.3. For Al0.3Ga0.7N/GaN heterojunctions, electron mobility values up to 1650 and 4400 cm2/V s were measured at 300 and 15 K, respectively. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371602
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of InP substrate misorientation on GaInAs-AlInAs interface and alloy quality (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3476-3480 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The quality of GaInAs-AlInAs epitaxial layers is found to be critically dependent on the degree of (100)-InP substrate misorientation. The alloy quality of both materials is improved when the substrate is misoriented 4° off the (100). The heterojunction interface quality as determined by the full width at half-maximum of quantum-well photoluminescence is also improved when a substrate misoriented by 4° is used. A degradation of both alloy and interface quality as compared to material on (100) InP is observed when the misorientation is 2°. These effects are also observed for strained quantum-well structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341482
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  • 3
    Electronic Resource
    Electronic Resource
    Metalorganic chemical vapor deposition of GaN on Si(111): Stress control and application to field-effect transistors (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7846-7851 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two schemes of nucleation and growth of gallium nitride on Si(111) substrates are investigated and the structural and electrical properties of the resulting films are reported. Gallium nitride films grown using a 10–500 nm-thick AlN buffer layer deposited at high temperature (∼1050 °C) are found to be under 260–530 MPa of tensile stress and exhibit cracking, the origin of which is discussed. The threading dislocation density in these films increases with increasing AlN thickness, covering a range of 1.1 to 〉5.8×109 cm−2. Films grown using a thick, AlN-to-GaN graded buffer layer are found to be under compressive stress and are completely crack free. Heterojunction field effect transistors fabricated on such films result in well-defined saturation and pinch-off behavior with a saturated current of ∼525 mA/mm and a transconductance of ∼100 mS/mm in dc operation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1372160
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  • 4
    Electronic Resource
    Electronic Resource
    Structural evolution in epitaxial metalorganic chemical vapor deposition grown GaN films on sapphire (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1541-1543 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structural evolution of epitaxial GaN layers grown on basal plane sapphire has been studied by atomic force microscopy (AFM), x-ray diffraction, and transmission electron microscopy (TEM). High-temperature growth (1050–1080 °C) on optimized nucleation layers leads to clear, specular films. AFM on the as-grown surface shows evenly spaced monatomic steps indicative of layer by layer growth. AFM measurements show a step termination density of 1.7×108 cm−2 for 5 μm films. This value is in close agreement with TEM measurements of screw and mixed screw-edge threading dislocation density. The total measured threading dislocation density in the 5 μm films is 7×108 cm−2. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114486
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of doping variations on electron transport in GaAs n+-n-n+ structures (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5695-5701 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron transport properties in GaAs n+-n-n+ structures with varying doping profiles (in the direction of electron transport) are investigated using self-consistent ensemble Monte Carlo simulations. In particular, we study the effects of ramp doping [i.e., linearly increasing (ramp-up) or decreasing (ramp-down) doping density within the n region] and spike doping (i.e., introducing one or more n+ spikes in the n region) on electron transport to assess differences, advantages, and potential applications of these doping profiles on device performance. Underlying physical mechanisms for electron transport in these structures are analyzed. Simulation results reveal that overall electron transport can be improved significantly by employing ramp-up (rather than ramp-down) doping and multispike (instead of single-spike) doping schemes. Potential advantages of variable doping in field-effect transistor applications include enhanced current drive capability, reduced source resistance, and improved breakdown characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351920
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  • 6
    Electronic Resource
    Electronic Resource
    Reactive removal of misfit dislocations from InGaAs on GaAs by lateral oxidation (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 845-847 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Layers of hypercritical thickness InGaAs/AlAs/GaAs have been shown to strain relax when the underlying AlAs layer is laterally oxidized. InxGa1−xAs layers of composition 0.2≤x≤0.4 have been investigated at thicknesses in the range 5–20 times the Matthews–Blakeslee critical thickness hc. The amount of strain relieved does not depend on the InGaAs-layer thickness, the initial strain state, or the composition of the material, but it does strongly depend on the oxidation temperature. The structure of the strain-relaxed InGaAs layer has been investigated using plan-view transmission electron microscopy. It is shown that the misfit dislocation density in In0.3Ga0.7As grown to 15 times the critical thickness (660 Å) has been reduced by two orders of magnitude after lateral oxidation. It is proposed that this is due to interfacial oxidation, which consumes the misfit dislocation cores. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1306918
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  • 7
    Electronic Resource
    Electronic Resource
    Polarization effects, surface states, and the source of electrons in AlGaN/GaN heterostructure field effect transistors (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 250-252 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The origin of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructure field effect transistors is examined theoretically and experimentally. Based on an analysis of the electrostatics, surface states are identified as an important source of electrons. The role of the polarization-induced dipole is also clarified. Experimental Hall data for nominally undoped Al0.34Ga0.66N/GaN structures indicate that ∼1.65 eV surface donors are the actual source of the electrons in the 2DEG, which forms only when the barrier thickness exceeds 35 Å. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126940
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  • 8
    Electronic Resource
    Electronic Resource
    Mg doping of GaN layers grown by plasma-assisted molecular-beam epitaxy (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 718-720 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaN:Mg layers grown by plasma-assisted molecular-beam epitaxy at 650 °C are investigated. Secondary-ion-mass-spectroscopy measurements reveal uniform Mg doping profiles with very sharp boundaries. The amount of incorporated Mg atoms changes approximately linearly with incident Mg flux. Hall measurements on p-type GaN:Mg layers show that about 1%–2% of all Mg atoms are ionized at room temperature. The hole mobility depends strongly on the hole concentration, varying from μp=24 cm2/V s for p=1.8×1017 cm−3 to μp=7.5 cm2/V s for p=1.4×1018 cm−3. GaN p–n diodes with molecular-beam-epitaxy-grown p regions are analyzed using current–voltage measurements. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125872
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  • 9
    Electronic Resource
    Electronic Resource
    High voltage operation (〉80 V) of GaN bipolar junction transistors with low leakage (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2457-2459 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have demonstrated the high voltage operation of n-p-n GaN bipolar junction transistors using regrown emitters. Devices were grown by metalorganic chemical vapor deposition on sapphire substrates. The n-type emitter was grown selectively on a base-collector p-n junction diode using a dielectric mask. A thin base (1000 Å) was used to increase the current gain over our previous result with a regrown emitter [J. B. Limb, L. McCarthy, P. Kozodoy, H. Xing, J. Ibbetson, Y. Smorchkova, S. P. DenBaars, and U. K. Mishra, Electron. Lett. 35, 19 (1999)]. The base contacts were better than expected despite the use of a thin base. Common emitter operation showing a voltage operation of over 80 V with negligible leakage has been demonstrated. Room temperature current gain was ∼3 corresponding to a current transfer ratio of ∼0.75. This results in a calculated minority carrier lifetime of about 80 pS in the base. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126375
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of growth termination conditions on the performance of AlGaN/GaN high electron mobility transistors (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3088-3090 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of the growth conditions of the top 2.5 nm thick AlGaN cap layer and wafer cool down conditions on AlGaN/GaN high electron mobility transistor performance was investigated. The AlGaN/GaN heterostructures were deposited on sapphire by metalorganic chemical vapor deposition and consisted of a 3 μm thick semi-insulating GaN layer and an 18 nm thick Al0.33Ga0.67N layer, the top 2.5 nm of which was deposited under various conditions. The power performance of the devices severely degraded for all samples where the Al content of the top 2.5 nm of AlGaN was increased and/or the ammonia flow during growth of the top layer was decreased. A modest improvement in the output power density was observed when the growth conditions of the cap layer were identical of those of the rest of the AlGaN layer, but when the wafer was cooled down in pure nitrogen. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1372620
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