Effective heat dissipation is the bottleneck problem for the development and commercialization of GaN-based high-power electronic and photonic devices. To address this challenge and explore the underlying mechanism of phonon transportation across the GaN/AlN heterointerface, in this work, we formed three types of GaN/AlN heterostructures with distinctively different interfacial morphologies by annealing recrystallization approach. It is found that the interfacial thermal conductance (ITC) of GaN/AlN heterostructures can be remarkably improved by tailoring the interfacial crystal structure and phase morphology. Besides the commonly amorphous phase and ideal ordered wurtzite phase, we further found that AlN may present an additional stable rock salt phase at the interfacial region, and its significant effect on interfacial thermal transport has been observed. Using molecular dynamics simulation, we systematically investigated the effects of different GaN/AlN heterojunctions on the ITCs. Our results suggest that heat dissipation at the GaN/AlN interface is dominated by phonons scattered diffusely by the amorphous region at interfaces and the ITC can be significantly enhanced by recrystallizing the amorphous AlN to rock salt one. Furthermore, through phonon vibrational spectrum, we revealed that phonon modes dominate the energy transport across the interfaces of wurtzite AlN/GaN, amorphous AlN/GaN, and rock salt AlN/GaN are significantly different. Finally, we found the ITC increased with the temperature due to the enhanced inelastic phonon scattering and the presence of additional excited phonon modes at higher temperatures. The findings elucidated here provide a clearer insight into the effect of interfacial microstructures on the interfacial thermal resistance of GaN–substrate interface, which also provide a viable heat management strategy for the high-power GaN-based devices.

Interfacial engineering for the enhancement of interfacial thermal conductance in GaN/AlN heterostructure

Silicon photonics in the near-IR, up to 1.6 µm, is already one of key technologies in optical data communications, particularly short range. It also is being prospected for applications in quantum computing, artificial intelligence, optical signal processing, where complex photonic integration is to be combined with a large-volume fabrication. However, silicon photonics does not yet cover a large portion of applications in the mid-IR. In the wavelength range of 2–5 µm, environmental sensing, life sensing and security, all rely on optical signatures of molecular vibrations to identify complex individual chemical species. The markets for such analysis are huge and constantly growing, with a push for sensitivity, specificity, compactness, low-power operation and low cost. An all-group-IV, CMOS-compatible mid-IR integrated photonic platform would be a key enabler in this wavelength range. As for other wavelengths, such a platform should be complete with low-loss guided interconnects, detectors, eventually modulators, and most important an efficient and integrated light sources. This chapter reviews the recent developments of mid-IR silicon-compatible optically and electrically pumped lasers, light emitting diodes and photodetectors based on Ge, GeSn and SiGeSn alloys. It contains insights into the fundamentals of these developments, including bandstructure modelling, material growth and processing techniques.

Lasing in Group-IV Materials

An In-Depth Study of the Boron and Phosphorous Doping of GeSn

Growth of millimeter wave AlN/GaN heterostructures by MOCVD

Effect of spiral-like islands on structural quality, optical and electrical performance of InGaN/GaN heterostructures grown by metal organic chemical vapour deposition

Si:B or Ge:B layers can used to fabricate devices such as p-type metal oxide semiconductor transistors, photo-detectors, light emitting diodes and so on. We have explored here the in-situ boron-doping of Si and Ge with Si2H6 + B2H6 and Ge2H6 + B2H6. Such chemistries enable Si or Ge epitaxy at temperatures definitely lower than with mainstream precursors such as SiH4 or GeH4. Growth temperatures and pressures in our 200mm Reduced Pressure - Chemical Vapor Deposition tool were 550°C, 20 Torr (Si) and 350°C, 100 Torr (Ge). X-ray Diffraction was used to convert the tensile strain in Si:B or Ge:B layers into substitutional B concentrations, while Secondary Ions Mass Spectrometry gave us the atomic B concentration. As far as Si:B was concerned, a huge growth rate increase (from 9.5 up to 39.8 nm min.-1) was evidenced when adding relatively small amounts of B2H6 to Si2H6. Ultra-high substitutional and atomic boron contents were obtained in those Si:B layers (at most: 2.7x1020 and 1.1x1021 atoms cm-3). For higher B2H6 flows, films became poly-crystalline. A similar growth rate increase (from 5.8 up to 20.8 nm min.-1) and really high substitutional B concentrations (at most: 4.8x1020 atoms cm-3) were otherwise obtained for Ge:B. Such concentrations were several times higher than with conventional chemistries.

Ultra-High Boron Doping of Si and Ge for Nanoelectronics and Photonics

Unravelling the unwanted Ga incorporation effect on InGaN epilayers grown in CCS MOVPE reactors

We have benchmarked germane and digermane for the growth of pseudomorphic GeSn layers on Ge Strain-relaxed Buffers, themselves on Si(001) substrates. For a fixed GeH4 partial pressure (1.28 Torr), the GeSn Growth Rate (GR) increased linearly with the SnCl4 flow at 349°C. That increase was sub-linear at 325°C. The Sn content was almost steady with the SnCl4 flow at 349°C. Meanwhile, it increased then decreased at 325°C. We otherwise had exponential increases, over the 301°C - 349°C range, of the GeSn GR with the temperature, with similar activation energies around 10 kcal mol.-1 for both chemistries. In contrast, the Sn content linearly decreased as the temperature increased, with a slope which was less for GeH4 than for Ge2H6 (- 1.0% / 10°C instead of - 1.7% / 10°C). Although the GeH4 flow was 4 times the Ge2H6 one and the chamber pressure 4 times higher (400 Torr versus 100 Torr), GeSn GR were almost the same for a given SnCl4 flow. Sn contents were by contrast significantly lower with GeH4 than with Ge2H6. Halving, for the same GeH4 flow, the SnCl4 flow resulted in GeSn GR 40% lower but slighly higher Sn contents, which was once again counterintuitive. GeSn layers were flat and of high crystalline quality with both chemistries. Finally, while the GeSn GR and Sn contents were rather uniform over the 200mm wafer surface with Ge2H6+SnCl4, the situation was definitely worse with GeH4+SnCl4. GR were then significantly higher at the wafer edges than close to the center.

Epitaxy of Pseudomorphic GeSn Layers with Germane (GeH4) or Digermane (Ge2H6) as Ge Precursors and Tin Tetrachloride (SnCl4) as the Sn Precursor

Impact of growth conditions on AlN/GaN heterostructures with in-situ SiN capping layer

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Papers

Ultra-High Boron Doping of Si and Ge for Nanoelectronics and Photonics

Unravelling the unwanted Ga incorporation effect on InGaN epilayers grown in CCS MOVPE reactors

Epitaxy of Pseudomorphic GeSn Layers with Germane (GeH4) or Digermane (Ge2H6) as Ge Precursors and Tin Tetrachloride (SnCl4) as the Sn Precursor

Impact of growth conditions on AlN/GaN heterostructures with in-situ SiN capping layer