Papers by SEBASTIAN TAMARIZ
HAL (Le Centre pour la Communication Scientifique Directe), Sep 4, 2022
MBE has several advantages for the epitaxy of GaN-based heterostructures. More specifically, by c... more MBE has several advantages for the epitaxy of GaN-based heterostructures. More specifically, by controlling the interface between the AlN buffer layer and the silicon substrate, ammonia-MBE allows to grow innovative structures on silicon. Epitaxy on silicon necessarily requires a demonstration of scaling-up on large wafers used by the microelectronics industry. Properties of several epitaxial heterostructures grown on 200 mm substrate are presented and discussed, emphasizing the originality of these structures and the beneficial contribution of MBE. Also, prospects and future challenges are discussed.
HAL (Le Centre pour la Communication Scientifique Directe), Oct 9, 2022
MBE has several advantages for the epitaxy of GaN-based heterostructures. More specifically, by c... more MBE has several advantages for the epitaxy of GaN-based heterostructures. More specifically, by controlling the interface between the AlN buffer layer and the silicon substrate, ammonia-MBE allows to grow innovative structures on silicon. Epitaxy on silicon necessarily requires a demonstration of scaling-up on large wafers used by the microelectronics industry. Properties of several epitaxial heterostructures grown on 200 mm substrate are presented and discussed, emphasizing the originality of these structures and the beneficial contribution of MBE. Also, prospects and future challenges are discussed.
We present an overview on the growth and the optical properties of GaN quantum dots (QDs) embedde... more We present an overview on the growth and the optical properties of GaN quantum dots (QDs) embedded in planar AlN grown on the following three different types of substrates: single AlN crystal, AlN on sapphire, and AIN on Si(111). QD density control over three orders of magnitude from 108 to 1011 cm−2 is demonstrated by changing the GaN growth rate. After having established a phase diagram for the QD formation and the critical thickness for the 2D-3D transition, we focus on a comparative study on the optical fingerprint of individual QDs. We identify numerous excitonic complexes in individual GaN QDs and analyze their suitability for single-photon emission at non-cryogenic temperatures as attested by the corresponding $\mathrm{g}^{(2)}$ -traces derived from photon correlation measurements. Clear antibunching with $\mathrm{g}^{(2)}(0)=0.17\pm 0.03$ is observed at 300 K, which originates from the decay of single excitons in an individual GaN QD. Finally, an excitation power dependent analysis of the photon statistics reveals the limiting factors for the purity of our single photon sources, provides insight into the physical mechanism of spectral diffusion, and a general pathway towards future optimization, which aims for electrically driven single photon sources operating at 300 K.
Light-Science & Applications, Apr 28, 2022
III-nitride quantum dots (QDs) are a promising system actively studied for their ability to maint... more III-nitride quantum dots (QDs) are a promising system actively studied for their ability to maintain single photon emission up to room temperature. Here, we report on the evolution of the emission properties of self-assembled GaN/ AlN QDs for temperatures ranging from 5 to 300 K. We carefully track the photoluminescence of a single QD and measure an optimum single photon purity of g (2) (0) = 0.05 ± 0.02 at 5 K and 0.17 ± 0.08 at 300 K. We complement this study with temperature dependent time-resolved photoluminescence measurements (TRPL) performed on a QD ensemble to further investigate the exciton recombination dynamics of such polar zero-dimensional nanostructures. By comparing our results to past reports, we emphasize the complexity of recombination processes in this system. Instead of the more conventional mono-exponential decay typical of exciton recombination, TRPL transients display a bi-exponential feature with short-and long-lived components that persist in the low excitation regime. From the temperature insensitivity of the long-lived excitonic component, we first discard the interplay of dark-to-bright state refilling in the exciton recombination process. Besides, this temperature-invariance also highlights the absence of nonradiative exciton recombinations, a likely direct consequence of the strong carrier confinement observed in GaN/ AlN QDs up to 300 K. Overall, our results support the viability of these dots as a potential single-photon source for quantum applications at room temperature.
ACS Photonics, Apr 28, 2020
Quantum dots (QDs) based on III-nitride semiconductors are promising for single photon emission a... more Quantum dots (QDs) based on III-nitride semiconductors are promising for single photon emission at noncryogenic temperatures due to their large exciton binding energies. Here, we demonstrate GaN QD single photon emitters operating at 300 K with g (2) (0) = 0.17 ± 0.08. At this temperature, single photon emission rates up to 10 6 s −1 are reached, while g (2) (0) ≤ 0.5 is maintained. Our results are achieved for GaN QDs embedded in a planar AlN layer grown on silicon, representing a promising pathway for future interlinkage with optical waveguides and cavities. These samples allow exploring the limiting factors to key performance metrics for single photon sources, such as brightness and single photon purity. While high brightness is assured by large exciton binding energies, the single photon purity is mainly affected by the spectral overlap with the biexcitonic emission. Thus, the performance of a GaN QD as a single photon emitter depends on the balance between the emission line width and the biexciton binding energy. Small GaN QDs with an emission energy in excess of 4.2 eV are promising candidates for future room temperature applications, since the biexciton binding energy becomes comparable to the average emission line width of around 55 meV.
Journal of Crystal Growth, Oct 1, 2017
Abstract We present a comprehensive study of AlN growth on Si(1 1 1) substrate by gas source mole... more Abstract We present a comprehensive study of AlN growth on Si(1 1 1) substrate by gas source molecular beam epitaxy with ammonia as nitrogen precursor in the high temperature range. We first demonstrate that the observation of the silicon 7 × 7 surface reconstruction by reflection high energy electron diffraction can be misleading as this technique is not sensitive to low density surface defects like SiC crystallites. A careful in situ cleaning procedure with annealing cycles at 1100 °C allows getting rid of any surface defects, as shown by atomic force microscopy imaging. Then, we explore the effect of the growth temperature on the surface morphology and structural properties of 100 nm thick AlN epilayers. At 1200 °C, the growth proceeds with the step flow mode regime, which induces spiral-growth around screw-type dislocations and therefore surface roughening. On the other hand, a smooth surface morphology can be achieved by setting the temperature at 1100 °C, which corresponds to the growth mode transition from two-dimensional nucleation to step flow. A further decrease of the growth temperature to 900 °C leads to surface defects ascribed to polarity inversion domains. Similar defects are observed for growths performed at 1100 °C when the NH 3 flow is reduced below 100 sccm. This points out the sensitivity of AlN to the surface stoichiometry.
The rapidly increasing power demand, downsizing of power electronics and material specific perfor... more The rapidly increasing power demand, downsizing of power electronics and material specific performance limitation of silicon has led to the development of AlGaN/GaN heterostructures for high power applications. In this frame, emerging AlxGa1-xN channel based heterostructures show promising features for next generation of power electronics. In this work, we propose the study of breakdown field variation through the AlGaN channel HEMTs-on-Silicon with various Al composition. The fabricated devices exhibited remarkable buffer breakdown field > 2.5 MV/cm for sub-micron heterostructures grown on silicon substrate. Furthermore, we also experimentally demonstrate that Al-rich AlGaN channel enable both boosting the 3-terminal transistor breakdown voltage and also benefiting from a superior thermal stability.
Physica Status Solidi A-applications and Materials Science, May 9, 2023
Submicrometer‐thick AlGaN/GaN high‐electron‐mobility transistor (HEMT) epilayers grown on silicon... more Submicrometer‐thick AlGaN/GaN high‐electron‐mobility transistor (HEMT) epilayers grown on silicon substrate with a state‐of‐the art vertical buffer breakdown field as high as 6 MV cm−1 enabling a high transistor breakdown voltage of 250 V for short gate‐to‐drain distances despite such a thin structure are reported. HEMTs with a gate length of 100 nm exhibit good DC characteristics with a low drain‐induced barrier, going as low as 100 mV V−1 for a VDS of 30 V. Breakdown voltages of each epilayer from the decomposed heterostructure reveals that the outstanding breakdown strength is attributed to the insertion of Al‐rich AlGaN in the buffer layers combined with an optimized AlN nucleation layer. As a result, large signal measurements at 10 GHz could be reliably achieved up to VDS = 35 V despite the use of a 100 nm gate length. These results demonstrate the potential of submicrometer‐thick buffer GaN‐on‐Si heterostructures for high‐frequency applications.
arXiv (Cornell University), Jan 27, 2020
Quantum dots (QDs) based on III-nitride semiconductors are promising for single photon emission a... more Quantum dots (QDs) based on III-nitride semiconductors are promising for single photon emission at non-cryogenic temperatures due to their large exciton binding energies. Here, we demonstrate GaN QD single photon emitters operating at 300 K with g (2) (0) = 0.17±0.08 under continuous wave excitation. At this temperature, single photon emission rates up to 6 × 10 6 s −1 are reached while g (2) (0) ≤ 0.5 is maintained. Our results are achieved for GaN QDs embedded in a planar AlN layer grown on silicon, representing a promising pathway for future interlinkage with optical waveguides and cavities. These samples allow exploring the limiting factors to key performance metrics for single photon sources, such as brightness and single photon purity. While high brightness is assured by large exciton binding energies, the single photon purity is mainly affected by the spectral overlap with the biexcitonic emission. Thus, the performance of a GaN QD as a single photon emitter depends on the balance between the emission linewidth and the biexciton binding energy. We identify small GaN QDs with an emission energy in excess of 4.2 eV as promising candidates for future room temperature applications, since the biexciton binding energy becomes comparable to the average emission linewidth of around 55 meV.
Applied Physics Letters, Feb 25, 2019
Graphene-assisted quasi-van der Waals epitaxy of AlN film for ultraviolet light emitting diodes o... more Graphene-assisted quasi-van der Waals epitaxy of AlN film for ultraviolet light emitting diodes on nano-patterned sapphire substrate
Journal of Applied Physics, Feb 5, 2021
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Electronics
In this work, sub-micron-thick AlN/GaN transistors (HEMTs) grown on a silicon substrate for high-... more In this work, sub-micron-thick AlN/GaN transistors (HEMTs) grown on a silicon substrate for high-frequency power applications are reported. Using molecular beam epitaxy, an innovative ultrathin step-graded buffer with a total stack thickness of 450 nm enables one to combine an excellent electron confinement, as reflected by the low drain-induced barrier lowering, a low leakage current below 10 µA/mm and low trapping effects up to a drain bias VDS = 30 V while using sub-150 nm gate lengths. As a result, state-of-the-art GaN-on-silicon power performances at 40 GHz have been achieved, showing no degradation after multiple large signal measurements in deep class AB up to VDS = 30 V. Pulsed-mode large-signal characteristics reveal a combination of power-added efficiency (PAE) higher than 35% with a saturated output power density (POUT) of 2.5 W/mm at VDS = 20 V with a gate-drain distance of 500 nm. To the best of our knowledge, this is the first demonstration of high RF performance achie...
physica status solidi (a)
Submicrometer‐thick AlGaN/GaN high‐electron‐mobility transistor (HEMT) epilayers grown on silicon... more Submicrometer‐thick AlGaN/GaN high‐electron‐mobility transistor (HEMT) epilayers grown on silicon substrate with a state‐of‐the art vertical buffer breakdown field as high as 6 MV cm−1 enabling a high transistor breakdown voltage of 250 V for short gate‐to‐drain distances despite such a thin structure are reported. HEMTs with a gate length of 100 nm exhibit good DC characteristics with a low drain‐induced barrier, going as low as 100 mV V−1 for a VDS of 30 V. Breakdown voltages of each epilayer from the decomposed heterostructure reveals that the outstanding breakdown strength is attributed to the insertion of Al‐rich AlGaN in the buffer layers combined with an optimized AlN nucleation layer. As a result, large signal measurements at 10 GHz could be reliably achieved up to VDS = 35 V despite the use of a 100 nm gate length. These results demonstrate the potential of submicrometer‐thick buffer GaN‐on‐Si heterostructures for high‐frequency applications.
HAL (Le Centre pour la Communication Scientifique Directe), May 3, 2022
Advances in Ultrafast Condensed Phase Physics III
Light: Science & Applications
III-nitride quantum dots (QDs) are a promising system actively studied for their ability to maint... more III-nitride quantum dots (QDs) are a promising system actively studied for their ability to maintain single photon emission up to room temperature. Here, we report on the evolution of the emission properties of self-assembled GaN/AlN QDs for temperatures ranging from 5 to 300 K. We carefully track the photoluminescence of a single QD and measure an optimum single photon purity of g(2)(0) = 0.05 ± 0.02 at 5 K and 0.17 ± 0.08 at 300 K. We complement this study with temperature dependent time-resolved photoluminescence measurements (TRPL) performed on a QD ensemble to further investigate the exciton recombination dynamics of such polar zero-dimensional nanostructures. By comparing our results to past reports, we emphasize the complexity of recombination processes in this system. Instead of the more conventional mono-exponential decay typical of exciton recombination, TRPL transients display a bi-exponential feature with short- and long-lived components that persist in the low excitatio...
Journal of Applied Physics, 2021
c-plane GaN/AlN quantum dots (QDs) are promising zero-dimensional quantum nanostructures that exh... more c-plane GaN/AlN quantum dots (QDs) are promising zero-dimensional quantum nanostructures that exhibit single photon emission properties up to room temperature and even above. In this context, it is of prime interest to gain a deeper insight into the recombination dynamics of photogenerated electron–hole pairs captured by such dots. Hence, in this work, we study the time-resolved photoluminescence (PL) properties in the low injection regime and at cryogenic temperatures of c-plane GaN/AlN QD ensembles emitting above the bulk GaN bandgap in order to properly understand the nature of the recombination channels behind the observed non-exponential decay time profiles. Such decays reveal the existence of a relaxation channel competing with the radiative recombination one. It is thus observed that for the former process the dynamics is independent of the dot height, which is attributed to a reversible nonradiative transfer that could be mediated by a spin-flip process to a dark-level state...
2019 Compound Semiconductor Week (CSW), 2019
We present an overview on the growth and the optical properties of GaN quantum dots (QDs) embedde... more We present an overview on the growth and the optical properties of GaN quantum dots (QDs) embedded in planar AlN grown on the following three different types of substrates: single AlN crystal, AlN on sapphire, and AIN on Si(111). QD density control over three orders of magnitude from 108 to 1011 cm−2 is demonstrated by changing the GaN growth rate. After having established a phase diagram for the QD formation and the critical thickness for the 2D-3D transition, we focus on a comparative study on the optical fingerprint of individual QDs. We identify numerous excitonic complexes in individual GaN QDs and analyze their suitability for single-photon emission at non-cryogenic temperatures as attested by the corresponding $\mathrm{g}^{(2)}$ -traces derived from photon correlation measurements. Clear antibunching with $\mathrm{g}^{(2)}(0)=0.17\pm 0.03$ is observed at 300 K, which originates from the decay of single excitons in an individual GaN QD. Finally, an excitation power dependent analysis of the photon statistics reveals the limiting factors for the purity of our single photon sources, provides insight into the physical mechanism of spectral diffusion, and a general pathway towards future optimization, which aims for electrically driven single photon sources operating at 300 K.
Uploads
Papers by SEBASTIAN TAMARIZ