Metalorganic chemical vapor deposition of high mobility AlGaN/GaN heterostructures

Abstract

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.

Excitonic localization in AlN-rich AlxGa1−xN/AlyGa1−yN multi-quantum-well grain boundaries

“…This can also increase the probability of TD annihilation due to the intersections of these dislocations with their opposite Burgers vector equivalents. 10 Keller et al 3 highlighted a similar outcome in AlGaN/GaN epilayers.…”

“…Excitonic localization in AlN-rich Al x Ga 12x N/Al y Ga 12y N multi-quantum-well grain boundaries Idris A. Ajia, 1 P. R. Edwards, 2 Z. Liu, 3 J. C. Yan, 3 R. W. Martin, 2 AlGaN-based deep ultraviolet (UV) devices have a wide range of applications, from their use in high-density recording devices to water sterilization. Additionally, there are other high-power and high-temperature applications, due to their thermal and mechanical durability.…”

“…3,4 Due to the small disparity in the interatomic spacing of Al and Ga atoms, AlGaN is generally not expected to exhibit the kind of immiscibility that characterizes InGaNbased materials. 5,6 As such, the rough surface of the material is typically attributed to lateral compositional fluctuation, which is related to the slow lateral growth rate of Al adatoms during deposition.…”

Influence of Al content on electrical and structural properties of Si‐doped Al x Ga 1–x N/GaN HEMT structures

“…From the AFM measurements, the dark dots and tiny trenches are estimated to be several nanometers in thickness, smaller than the AlGaN barrier thickness. Keller et al [11] pointed out, that the defects did not form at the AlGaN/GaN interface but developed in a later stage of growth. Bougrioua et al [6] also investigated such defects and observed that they were V-shaped and originated from the strain in the AlGaN barrier layers.…”

Study on growth and electrical performance of double‐heterostructure AlGaN/GaN/AlGaN field‐effect‐transistors

“…Typically, buffer layers are being optimized to secure a sufficiently high resistive behavior, simultaneously minimizing the incorporation of deep traps. This optimization is typically achieved by appropriate deposition parameters [7] and by compensation doping using transition metals [8].…”