GaAs-Based Wide-Aperture Single Emitters with 68 W Output Power at 69% Efficiency Realized Using a Periodic Buried-Regrown-Implant-Structure

Increased optical output power
$P_{\text{opt}}$
from single broad area GaAs-based diode lasers is demanded for material processing, with higher
$P_{\text{opt}}$
and cost reduction in
$/\mathrm{W}$
enabled by using devices with ever-wider apertures [1]. Device structures suitable for single emitters with very large footprints
$(> 4\ \text{mm}^{2})$
that sustain high
$P_{\text{opt}}$
and conversion efficiency
$\eta_{\mathrm{E}}$
without exciting unwanted optical modes (e.g. ring oscillations) are also of interest as an enabling technology for high power photonic crystal surface emitting lasers [2]. We report here progress in broad area diode lasers with resonator length
$L=4$
mm and emitting aperture of
$W=1200\ \mu \mathrm{m}$
with wavelength
$\lambda$
= 915 nm. An
$\eta_{\mathrm{E}}$
-optimized highly vertically asymmetric epitaxial design was used, taken from [3]–[5], and grown using metal organic vapor phase epitaxy (MOVPE). To suppress lateral (e.g. ring) oscillations, following [6], the lateral current path was patterned periodically, with 9
$\mu \mathrm{m}$
current blocking stripes on a 29
$\mu \mathrm{m}$
period. Here, the lateral pattern was realised with a buried-regrown-implant-structure, BRIS, following [3]–[5], see schematic in Fig. 1a. After the first growth the p-side cladding and waveguide layers of the laser are implanted with
$\mathrm{O}^{+}$
ions to block current flow, periodically within the stripe, and broadly outside the stripe, then the wafer is regrown to complete the structure. In contrast to approaches based on etched p-n junctions [7], the wafer is still planar, minimizing growth defects, and lateral refractive index steps are minimized. Thick (800 nm) highly-doped p-type material was regrown after implantation. The residual thickness is
$d_{\text{res}}\sim 600$
nm (offset between current blocking and active region), sufficient to suppress 70 … 80% of lateral current spreading at the device edges [7]. After regrowth, single emitters lasers were fabricated using standard techniques, facet passivated (ZnSe) then coated for front and rear facet reflectivity of
$R_{\mathrm{F}}=1.8\%$
and
$R_{\mathrm{R}}=98\%$
. The devices were mounted with AuSn in a miniaturised
$(6\times 8\times 3.2\ \text{mm})$
CuW -sandwich package. Fig. 1 b presents electro-optic characteristics at
$25^{\circ}\mathrm{C}$
heatsink temperature,
$P_{\text{opt}}$
is measured with a calibrated thermoelectric detector, in-pulse-power with a fast photodetector, voltage
$U$
in 4-terminal configuration and far field with a goniometer. In quasi-continuous wave QCW test (10 Hz, 500
$\mu \mathrm{s})$
, peak
$\eta_{\mathrm{E}}=P_{\text{opt}}/IU=69\%$
(current, I) at
$P_{\text{opt}}=68\ \mathrm{W}$
and
$\eta_{\mathrm{E}}=52\%$
at
$P_{\text{opt}}=200\ \mathrm{W}$
are seen. In CW test,
$P_{\text{opt}}=45\ \mathrm{W}$
at
$\eta_{\mathrm{E}}=56\%$
, thermally limited (thermal resistance
$R_{\text{th}}=1.1$
K/W, obtained from the wavelength shift). The CW lateral far-field is also shown in Fig. 1, and is
$\leq 12^{\circ}$
(95% power) up to
$P_{\text{opt}}=40\ \mathrm{W}$
, corresponding to a beam quality
$M^{2} < 250($
for
$W=1200\ \mu \mathrm{m})$
, suitable for low-loss coupling into a 1 mm NA 0.22 fiber. No evidence is seen for ring oscillations. Improved
$\eta_{\mathrm{E}}$
is obtained at comparable
$P_{\text{opt}}$
referred to earlier studies ([8]:
$W=800\ \mu \mathrm{m},L=3.6$
mm,
$\eta_{\mathrm{E}}=52\%$
at
$P_{\text{opt}}=50\ \mathrm{W})$
, in spite of the use of
$10\times$
smaller heatsink ([8]: 25
$\mathrm{x}\ 25$
mm). In Fig. 1 c, two far field peaks are observed up to
$P_{\text{opt}}=30\ \mathrm{W}$
, indicating the strong contribution of a super-mode with 29
$\mu \mathrm{m}$
period, which is sustained to higher
$P_{\text{opt}}$
than previously reported [9] (super-mode to
$P_{\text{opt}}=5 \ \mathrm{W}$
, periodic implant in contact for
$d_{\text{res}} > 1\ \mu \mathrm{m}$
), promising for realising high brightness device and resonator configurations [2], [10], [11].