We demonstrate state-of-the-art p-type (Al)GaN layers deposited at low temperature (740 °C) by ammonia molecular beam epitaxy (NH3-MBE) to be used as top cladding of laser diodes (LDs) with the aim of further reducing the thermal budget on the InGaN quantum well active region. Typical p-type GaN resistivities and contact resistances are 0.4 Ω cm and 5 × 10−4 Ω cm2, respectively. As a test bed, we fabricated a hybrid laser structure emitting at 400 nm combining n-type AlGaN cladding and InGaN active region grown by metal-organic vapor phase epitaxy, with the p-doped waveguide and cladding layers grown by NH3-MBE. Single-mode ridge-waveguide LD exhibits a threshold voltage as low as 4.3 V for an 800 × 2 μm2 ridge dimension and a threshold current density of ∼5 kA cm−2 in continuous wave operation. The series resistance of the device is 6 Ω and the resistivity is 1.5 Ω cm, confirming thereby the excellent electrical properties of p-type Al0.06Ga0.94N:Mg despite the low growth temperature.

The authors report the demonstration of a polarization-controlled vertical-cavity surface-emitting laser (VCSEL), emitting at the telecommunication wavelength. VCSELs are based on an active medium constituted of well elongated InAs quantum dashes (QDHs) nanostructures grown on conventional (001) oriented InP substrate. QDHs present important optical polarization anisotropies according to the [11¯0] crystallographic orientation. Inserted into a VCSEL microcavity, QDH VCSELs show a continuous wave laser operation at 1.6 μm, at room temperature, with a reduced 13 kW/cm2 optical excitation density threshold. The QDH VCSEL output laser polarization is fixed along the same [11¯0] direction. Power and temperature dependant measurements do not show any polarization instabilities and switching on all QDH VCSELs. A polarization extinction ratio as high as 30 dB is deduced from experiments.

Mahbub; Maaskant, Pleun P.; Frayssinet, E.; de Mierry, P.; Draeger, A. Rights

Passive mode-locked pulses with repetition frequencies in the range 40 to 90 GHz were observed in blue-violet GaN-based quantum-well lasers without external cavities. The lasers had two-section geometry with built-in saturable absorber section. The individual pulses had durations as short as 3-5 ps at peak powers of around 320 mW