J.-F. Carlin

High electron mobility lattice-matched AlInN∕GaN field-effect transistor heterostructures

Room temperature electron mobility of 1170cm2∕Vs is obtained in an undoped, lattice-matched, Al0.82In0.18N∕GaN field-effect transistor heterostructure, while keeping a high (2.6±0.3)×1013cm−2 electron gas density intrinsic to the Al0.82In0.18N∕GaN material system. This results in a two-dimensional sheet resistance of 210Ω∕◻. The high mobility of these layers, grown by metal-organic vapor phase epitaxy on sapphire substrate, is obtained thanks to the insertion of an optimized AlN interlayer, reducing the alloy related interface roughness scattering.

Two-dimensional electron gas density in Al1−xInxN/AlN/GaN heterostructures (0.03≤x≤0.23)

Compared to the AlGaN alloy, which can only be grown under tensile strain on GaN, the AlInN alloy is predicted by Vegards law to be lattice-matched (LM) on fully relaxed GaN templates for an indium content of ~17.5%, i.e., it can be grown either tensely or compressively on GaN. The effect of strain on the polarization induced sheet charge density at the Al1-x Inx N/AlN/GaN heterointerfaces is carefully investigated for 6 and 14 nm thick AlInN barriers including a 1 nm thick AlN interlayer. The barrier indium content ranges at 0.03=x=0.23 for 6 nm thick barriers and 0.07=x=0.21 for 14 nm thick barriers. It is found that the two-dimensional electron gas (2DEG) density varies between (3.5±0.1) × 1013 cm-2 and (2.2±0.1) × 1013 cm-2 for 14 nm thick barriers. Finally, a 2DEG density up to (1.7±0.1) × 1013 cm-2 is obtained for a nearly LM AlInN barrier with ~14.5% indium on GaN as thin as 6 nm.

Barrier-Layer Scaling of InAlN/GaN HEMTs

We discuss the characteristics of high-electron mobility transistors with barrier thicknesses between 33 and 3 nm, which are grown on sapphire substrates by metal-organic chemical vapor deposition. The maximum drain current (at VG = 2.0 V) decreased with decreasing barrier thickness due to the gate forward drive limitation and residual surface-depletion effect. Full pinchoff and low leakage are observed. Even with 3-nm ultrathin barrier, the heterostructure and contacts are thermally highly stable (up to 1000degC).

Crack-free fully epitaxial nitride microcavity using highly reflective AlInN∕GaN Bragg mirrors

We report the growth over 2 in. sapphire substrates of crack-free fully epitaxial nitride-based microcavities using two highly reflective lattice-matched AlInN∕GaN distributed Bragg reflectors (DBRs). The optical cavity is formed by an empty 3λ∕2 GaN cavity surrounded by AlInN∕GaN DBRs with reflectivities close to 99%. Reflectivity and transmission measurements were carried out on these structures, which exhibit a stopband of 28 nm. The cavity mode is clearly resolved with a linewidth of 2.3 nm. These results demonstrate that the AlInN∕GaN system is very promising for the achievement of strong light–matter interaction and the fabrication of nitride-based vertical cavity surface emitting lasers.

Midinfrared intersubband absorption in lattice-matched AlInN∕GaN multiple quantum wells

We report the observation of midinfrared intersubband (ISB) absorption in nearly lattice-matched AlInN∕GaN multiple-quantum-wells. A clear absorption peak is observed around 3μm involving transitions from the conduction band ground state to the first excited state. In addition to ISB absorption, photoluminescence experiments were carried out on lattice- matched AlInN∕GaN single quantum wells in order to determine the spontaneous polarization discontinuity between GaN and Al0.82In0.18N compounds. The experimental value is in good agreement with theoretical predictions. Our results demonstrate that the AlInN∕GaN system is very promising to achieve crack-free and low dislocation density structures dedicated to intersubband devices in the 2–4μm wavelength range.

Tuning InAs/GaAs quantum dot properties under Stranski-Krastanov growth mode for 1.3 μm applications

In this paper, we present a systematic study of the effect of growth parameters on the structural and optical properties of InAs quantum dot (QD) grown under Stranski-Krastanov mode by molecular beam epitaxy. The dot density is significantly reduced from 1.9x10(10) to 0.6x10(10) cm(-2) as the growth rate decreases from 0.075 to 0.019 ML/s, while the island size becomes larger. Correspondingly, the emission wavelength shifts to the longer side. By increasing the indium fraction in the InGaAs capping layer, the emission wavelength increases further. At indium fraction of 0.3, a ground state transition wavelength as long as 1.4 mum with the excited state transition wavelength of around 1.3 mum has been achieved in our dots. The optical properties of QDs with a ground state transition wavelength of 1.3 mum but with different growth techniques were compared. The QDs grown with higher rate and embedded by InGaAs have a higher intensity saturation level from excitation dependent photoluminescence measurements and a smaller intensity decrease from temperature dependent measurements. Finally, single mirror light emitting diodes with a QD embedded in InGaAs have been fabricated. The quantum efficiency at room temperature is 1.3%, corresponding to a radiative efficiency of 21.5%

Recent progress in the growth of highly reflective nitride-based distributed Bragg reflectors and their use in microcavities

The growth of highly-reflective nitride-based distributed Bragg reflectors (DBRs) and their use in vertical cavity structures is reviewed. We discuss the various nitride material systems employed to design Bragg mirrors and microcavities, namely the Al-x(Ga)(1-x)N/(Al)(y)Ga1-yN and the lattice-matched Al1-xInxN/GaN (x(ln) similar to 18%)-based systems. An emphasis on particular issues such as strain management, internal absorption, alloy morphology and contribution of leaky modes is carried out. Specific properties of the poorly known AlInN alloy such as the bandgap variation with In content close to lattice-matched conditions to GaN are reported. The superior optical quality of the lattice-matched AlInN/GaN system for the realization of nitride-based DBRs is demonstrated. The properties of nitride-based vertical cavity devices are also described. Forthcoming challenges such as the realization of electrically pumped vertical cavity surface emitting lasers and strongly coupled quantum microcavities are discussed as well, and in particular critical issues such as vertical current injection.

Crack-free highly reflective AlInN/AlGaN bragg mirrors for UV applications

We report the growth of highly reflective distributed Bragg reflectors (DBRs) in the UV region using the Al0.85In0.15N∕Al0.2Ga0.8N lattice-matched system. The DBRs were deposited on nearly strain-free Al0.2Ga0.8N templates to avoid strain-induced structural degradations. The appearance of cracks was then completely suppressed. The DBRs exhibit a reflectivity higher than 99% at a wavelength as short as ∼340nm and a stop band width of 215meV (20nm).

Recombination coefficients of GaN-based laser diodes

We measure the charge carrier recombination coefficients of InGaN quantum wells by analyzing the dynamical properties of (Al,In)GaN laser diodes emitting in the violet spectral range. Relaxation oscillations and turn-on delays are fitted to a rate equation model including a charge carrier density dependent recombination rate. Using optical gain spectroscopy we can directly determine the injection efficiency of the devices and thereby separate the effect of charge carrier leakage from that of carrier recombination. We find a third-order recombination coefficient of (4.5±0.9)×10-31cm6s-1 which is in agreement with theoretical predictions for phonon- and alloy-disorder-assisted Auger scattering.

High quality factor two dimensional GaN photonic crystal cavity membranes grown on silicon substrate

We report on the achievement of freestanding GaN photonic crystal L7 nanocavities with embedded InGaN/GaN quantum wells grown by metal organic vapor phase epitaxy on Si (111). GaN was patterned by e-beam lithography, using a SiO2 layer as a hard mask, and usual dry etching techniques. The membrane was released by underetching the Si (111) substrate. Micro-photoluminescence measurements performed at low temperature exhibit a quality factor as high as 5200 at ∼420u2009nm, a value suitable to expand cavity quantum electrodynamics to the near UV and the visible range and to develop nanophotonic platforms for biofluorescence spectroscopy.