Jean-François Carlin

Room temperature polariton lasing in a GaN∕AlGaN multiple quantum well microcavity

The authors report room temperature polariton lasing at λ∼345nm in a hybrid AlInN∕AlGaN multiple quantum well microcavity (MQW-MC) containing a GaN∕AlGaN MQW active region, i.e., the achievement under nonresonant optical excitation of coherent light emission of a macroscopic population of polaritons occupying the lowest energy state of the lower polariton branch. This was made possible by taking advantage of the efficient relaxation of polaritons in a MQW-MC exhibiting a large vacuum Rabi splitting ΩVRS=56meV.

205-GHz (Al,In)N/GaN HEMTs

We report 55-nm gate AlInN/GaN high-electron-mobility transistors (HEMTs) featuring a short-circuit current gain cutoff frequency of fT = 205 GHz at room temperature, a new record for GaN-based HEMTs. The devices source a maximum current density of 2.3 A/mm at VGS = 0 V and show a measured transconductance of 575 mS/mm, which is the highest value reported to date for nonrecessed gate nitride HEMTs. Comparison to state-of-the-art thin-barrier AlGaN/GaN HEMTs suggests that AlInN/GaN devices benefit from an advantageous channel velocity under high-field transport conditions.

InAlN/GaN HEMTs: a first insight into technological optimization

High-electron mobility transistors (HEMTs) were fabricated from heterostructures consisting of undoped In/sub 0.2/Al/sub 0.8/N barrier and GaN channel layers grown by metal-organic vapor phase epitaxy on (0001) sapphire substrates. The polarization-induced two-dimensional electron gas (2DEG) density and mobility at the In/sub 0.2/Al/sub 0.8/N/GaN heterojunction were 2/spl times/10/sup 13/ cm/sup -2/ and 260 cm/sup 2/V/sup -1/s/sup -1/, respectively. A tradeoff was determined for the annealing temperature of Ti/Al/Ni/Au ohmic contacts in order to achieve a low contact resistance (/spl rho//sub C/=2.4/spl times/10/sup -5/ /spl Omega//spl middot/cm/sup 2/) without degradation of the channels sheet resistance. Schottky barrier heights were 0.63 and 0.84 eV for Ni- and Pt-based contacts, respectively. The obtained dc parameters of 1-/spl mu/m gate-length HEMT were 0.64 A/mm drain current at V/sub GS/=3 V and 122 mS/mm transconductance, respectively. An HEMT analytical model was used to identify the effects of various material and device parameters on the InAlN/GaN HEMT performance. It is concluded that the increase in the channel mobility is urgently needed in order to benefit from the high 2DEG density.

Island formation in ultra-thin InAs/InP quantum wells grown by chemical beam epitaxy

We have studied the effect of growth interruptions on 2‐monolayers‐thick InAs/InP strained quantum wells (QW) grown by chemical beam epitaxy. The main feature is the formation of up to 8‐monolayers‐thick InAs islands during As2 annealing of the QW. Their formation is characterized by a two to three dimensional transition of the reflection high‐energy electron diffraction pattern and multiple‐lines photoluminescence spectra. An increase of a short range roughness at the InP‐InAs interface due to As2 annealing of InP is also observed.

Progress in AlInN–GaN Bragg reflectors: Application to a microcavity light emitting diode

We report on the progress in the growth of highly reflective AlInN-GaN distributed Bragg reflectors deposited by metalorganic vapor phase epitaxy. Al1-xInxN layers with an In content around x similar to 0.17 are lattice-matched to GaN, thus avoiding strain-related issues in the mirror while keeping a high refractive index contrast of about 7%. Consequently, a reflectivity value as high as 99.4% at 450 nm was achieved with a 40-pair crack-free distributed Bragg reflector. We measured an average absorption coefficient alpha [cm(-1)] in the AlInN-GaN Bragg reflectors of 43 +/- 14 cm(-1) at 450 nm and 75 +/- 19 cm(-1) at 400 nm. Application to blue optoelectronics is demonstrated through the growth of an InGaN-GaN microcavity light emitting diode including a 12-pair Al0.82In0.18N-GaN distributed Bragg reflector as bottom mirror. The device exhibits clear microcavity effects, improved directionality in the radiation pattern and an optical output power of 1.7 mW together with a 2.6% external quantum efficiency at 20 mA

Blue monolithic AlInN-based vertical cavity surface emitting laser diode on free-standing GaN substrate

We report on III-nitride based blue vertical cavity surface emitting lasers using defect-free highly reflective AlInN/GaN distributed Bragg reflectors grown on c-plane free-standing GaN substrates. Lasing is demonstrated at room temperature under pulsed electrical injection. The high lasing threshold current density still prevents devices from continuous wave lasing because of large self-heating. The reasons for such a high threshold are discussed and we show that it mainly comes from large light absorption in the indium tin oxide current spreading layer. Properly tuning both its thickness and its position with respect to the electrical field could remarkably decrease the threshold.

Toward ultrahigh-efficiency aluminum oxide microcavity light-emitting diodes: guided mode extraction by photonic crystals

In this paper, we present an improved version of microcavity light-emitting diodes, relying on the use of a low-index material, aluminum oxide. Our work addresses in particular the injection scheme required by the insulating nature of this oxide. The device we fabricated demonstrated efficiencies up to 28% in air, using only planar technology. In these structures, most of the emission is guided. We further propose to include photonic crystals to extract this guided light. The design of the photonic crystals are discussed and substantiated by photoluminescence-based experiments.

Testing the Temperature Limits of GaN-Based HEMT Devices

The high temperature stability of AlGaN/GaN and lattice-matched InAlN/GaN heterostructure FETs has been evaluated by a stepped temperature test routine under large-signal operation. While AlGaN/GaN high-electron mobility transistors (HEMTs) have failed in an operating temperature range of 500°C, InAlN/GaN HEMTs have been operated up to 900°C for 50 h (in vacuum). Failure is thought to be still contact metallization stability related, indicating an extremely robust InAlN/GaN heterostructure configuration.

Continuous-wave dual-wavelength lasing in a two-section vertical-cavity laser

A vertical-cavity surface-emitting laser with two monolithically grown cavities is presented. The three-terminal device allows current injection into the active regions of both cavities. Under various injection conditions, the device lases continuous wave on either one of the two longitudinal modes supported by the cavity, or on both wavelengths simultaneously. By using a constant injection current in the bottom cavity, and adjusting the current in the top cavity, the device shows all four possible emission states. These are the off states, lasing at the short wavelength /spl lambda//sub S/, at the long wavelength /spl lambda//sub L/, and at both /spl lambda//sub S/ and /spl lambda//sub L/ at the same time.

InAlN/GaN MOSHEMT With Self-Aligned Thermally Generated Oxide Recess

We report on lattice-matched InAlN/GaN MOSHEMTs with an oxide-filled recess, self-aligned to the gate prepared by thermal oxidation at 800degC in oxygen atmosphere. The device delivered a maximum current density of 2.4 A/mm. Pulse measurements showed no apparent lag effects, indicating a high-quality native oxide. This was confirmed by monitoring the radio-frequency load lines in the time domain. The MOSHEMT yielded a power density of 6 W/mm at a drain voltage as low as 20 V and at 4 GHz, a power added efficiency of 32% and an ft and f max of 61 and 112 GHz, respectively, illustrating the capability of such MOSHEMT to operate at high frequencies.