Novel 900 nm diode lasers with epitaxially stacked multiple active regions and tunnel junctions

Abstract

A multi-active-region bipolar-cascade edge-emitting laser emitting at nearly 900 nm is presented. The three active regions and two tunnel junctions located in a single waveguide core share the same third-order vertical mode. A slope efficiency of 3.6 W/A was measured with a threshold current density of 230 A/cm 2 . The epitaxial layer stack developed features with very low internal optical losses of 0.7 cm −1 . The voltage extrapolated to vanishing current is only 0.3 V larger than 3 times the voltage of 1.4 V originating from the photon energy.

Internally wavelength stabilized 910 nm diode lasers with epitaxially stacked multiple active regions and tunnel junctions

“…However, it is less than expected most likely caused by optical losses such as residual inter‐band absorption or interface scattering within the Bragg grating since the emission from the rear facet is low (0.1 W, compare Figure 4). The series resistance of 0.57 Ω (0.86 mΩcm 2 ) and the voltage extrapolated to zero current of 4.5 V are like the values reported in [5] for different devices from another wafer.…”

“…Figure 4). The series resistance of 0.57 (0.86 m cm 2 ) and the voltage extrapolated to zero current of 4.5 V are like the values reported in [5] for different devices from another wafer.…”

“…Ideally, the slope efficiency of such a nanostack laser is proportional to the number N of diodes, so that far above the threshold there is an N ‐fold increase of the optical power, compared to a single diode at the same injection current, at the expense of a correspondingly increased voltage. Recently, we reported the successful stacking of three active regions alternating with tunnel junctions in a single waveguide core instead of stacking independently working laser diodes [5]. In order to minimize the impact of the large absorption resulting from the highly doped tunnel junctions and to maximize modal gain, we designed the waveguide in such a way that the tunnel junctions and active regions were placed into the nodes and antinodes, respectively, of the intensity for the third‐order vertical mode.…”

“…Device structure and fabrication: The layer stack grown on a n-GaAs substrate by metalorganic vapour phase epitaxy, identical to the one reported in reference [5], consists of n-GaAs buffer, n-Al 0.5 Ga 0.5 As cladding (donator density N D = 1 × 10 18 cm -3 ), n-and p-Al 0.45 Ga 0.55 As optical confinement layers (N D = N A = 5 × 10 16 cm -3 ) around the active regions and tunnel junctions (TJs), p-Al 0.75 Ga 0.25 As cladding (acceptor density N A = 1 × 10 18 cm -3 ) and p-GaAs cap (N A = 2 × 10 19 cm -3 ). The three active InGaAs quantum wells (QWs) sandwiched between GaAsP spacer layers and the two GaAs TJs are placed into the antinodes and nodes, respectively, of the third vertically guided mode.…”

“…Other guided modes (including the fundamental mode) suffer under increased losses and decreased gain because of deviating positions of the antinodes and nodes. The vertical profiles of the refractive index, mode intensity and band edges are given in [5].…”