| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
II2, MBE Growth Study of AlInN and AlInN/GaN Heterostructures for Intersubband Device Applications |
| Author(s) |
Liang Tang, Geoff Gardner, Bob Colby, Rich Molnar, Colin Edmunds, Michael J. Manfra, Oana Malis |
| On-Site Speaker (Planned) |
Liang Tang |
| Abstract Scope |
Nitride semiconductors are promising candidates for high-speed intersubband optoelectronic devices due to the existence of large conduction band offsets (exceeding 1 eV) and sub-picosecond upper-level lifetimes. However heterostructures with high mole fraction AlGaN are difficult to grow due to the large lattice mismatch between AlN and GaN. Al0.82In0.18N lattice-matched to GaN presents an alternative barrier material that provides high conduction band offset and significant reduction in strain in thick device structures. Nevertheless, the growth of high quality AlInN is hampered by several factors including the vastly different optimal growth temperatures for AlN and InN and the tendency for phase segregation during growth. We present a systematic study of the growth of AlInN films and AlInN/GaN superlattices by MBE on [0001] GaN templates. Using RF-plasma conditions known to produce a nitrogen-limited growth rate of 6.5nm/min for GaN, we studied the impact of varying growth rate, III/N ratio, and doping on the structural and optical properties of thick AlInN layers and AlInN/GaN superlattices. Initial studies focused on lattice-matched samples grown in the nitrogen-rich regime at a substrate temperature of 530°C. It was found the growth rate increases linearly with increasing total metal (Al+In) flux up to a growth rate of 3.8nm/min. Here high quality films can be realized. However, when the metal flux was increased further, film quality deteriorated as measured by x-ray diffraction, suggesting the onset of large scale segregation. The origin of this abrupt change is currently under investigation. Our films are characterized by atomic force microscopy (AFM), high resolution x-ray diffraction (HRXRD), high resolution transmission electron microscopy (HRTEM) and optical absorption measurements of doped superlattices. Thick AlInN films (~200nm) display high quality ω-2θ x-ray data. Si-doped AlInN/GaN superlattices display relatively smooth surface morphology with an RMS roughness of 0.9nm over a 4micron x 4micron area and strong satellite peaks in x-ray diffraction. Interestingly, even in films that do not display evidence of large scale segregation in x-ray data, high angle annular dark field STEM imagining indicates phase contrast consistent with small length scale segregation. The length scale of the fluctuations is a few nanometers. This observation is further corroborated by plan view images which are also sensitive to fluctuations in Z. This data indicate that our MBE-grown AlInN layers are not completely homogeneous. Finally we present data of the Silicon doping dependence of intersubband absorption in AlInN/GaN superlattices. While it is generally known that high Si-doping (~1019-1020cm-3) is required to measure significant intersubband absorption in Nitride structures, a systematic study of impact of Si doping levels on absorption in AlInN/GaN heterostructures is still lacking. We vary the Si doping levels over several orders of magnitude (1018cm-3 to high 1020cm-3) and correlate doping with strength and linewidth of intersubband absorption. |
| Proceedings Inclusion? |
Undecided |