High power semiconductor laser diode
View Patent ↗Semiconductor laser diodes, particularly broad area single emitter (BASE) laser diodes of high light output powers are commonly used in opto-electronics. Light output power and stability of such laser diodes are of crucial interest and any degradation during normal use is a significant disadvantage. The present invention concerns an improved design of such laser diodes, the improvement in particular significantly minimizing or avoiding (front) end section degradation at very high light output powers by controlling the current flow in the laser diode in a defined way. This is achieved by controlling the carrier injection, i.e. the injection current, into the laser diode in a novel way by creating single current injection points along the laser diode's longitudinal extension, e.g. along the waveguide. Further, the supply current/voltage of each single or group of current injection point(s) may be separately regulated, further enhancing controllability of the carrier injection.
1. A high power semiconductor laser diode including a semiconductor body having an active region with two end sections and front and back facets terminating said end sections, a first injector over at least part of said semiconductor body for injecting electrons into said active region, a second injector located opposite said first injector over at least part of said semiconductor body for injecting holes into said active region, at least one of said injectors comprising a metallization layer and an electrical connection to said metallization layer, said electrical connection configured as a plurality of point contacts, or a ribbon contact, a distance of the electrical connection to said at least one of the end sections being at least half of an estimated effective penetration depth α eff of current spreading in said active region, and the metallization layer being sufficiently thin such that the degree of carrier injection in the active region decreases continuously throughout at least one of said end sections so as to provide reduced carrier density at at least one of said end sections compared to a section of the active region adjacent the at least one of said end sections,
wherein the semiconductor laser diode is a junction-side-down mounted broad area single emitter (BASE) laser diode in which a relatively thick substrate material is sandwiched between the metallization layer of the first injector and the active layer; and
wherein said effective penetration depth is based on an approximate analytic expression derived for the junction-side-down mounted BASE laser diode, the analytic expression being shown in the following equation:
α
eff
=
2
σ
cont
σ
sub
d
sub
d
cont
where:
σ cont is the conductivity of the metallization layer material;
σ sub is the conductivity of the substrate material;
d cont is the vertical thickness of the metallization layer material; and
d sub is the vertical thickness of the substrate material.
2. The laser diode according to claim 1 , wherein at least one of the end sections is the region of the laser diode between a facet and said electrical connection.
3. The laser diode according to claim 1 , wherein said plurality of point contacts is in the form of a plurality of singular electron or hole injection points extending closely spaced essentially along the length of said laser diode, a first one of said singular injection points being located at a predetermined distance from said front and/or said back facet.
4. The laser diode according to claim 1 , wherein the metallization layer is thinner in a portion adjacent one of the facets than in a portion further away from said facet.
5. The laser diode according to claim 1 , wherein the metallization layer is sufficiently thin such that at least one part adjacent to at least one end section imparts a voltage drop, thus providing at least one unpumped end section.
6. The laser diode according to claim 1 , wherein another of said injectors comprises a second metallization layer and an associated, shaped or unshaped second electrical connection.
7. The laser diode according to claim 1 , wherein said at least one injector comprises a plurality of wired contacts.
8. The laser diode according to claim 1 , wherein said electrical connection is in the form of a plurality of point contacts and the current to each of said point contacts is controlled to provide a controlled current pattern within the laser diode.
9. The laser diode according to claim 1 , further including an injection limiter for limiting the injection of carriers at at least one of said end sections, said injection limiter comprising an insulation layer covering a portion of the laser diode adjacent to a facet such as to further reduce current injection within at least a portion of an end section.
10. The laser diode according to claim 1 , wherein the distance of the electrical connection to the at least one of the end sections is at least 100 μm.
11. The laser diode according to claim 1 , wherein the distance of the electrical connection to the at least one of the end sections is at least 200 μm.
12. The laser diode according to claim 1 , wherein the distance of the electrical connection to the at least one of the end sections is at least 500 μm.
13. The laser diode according to claim 1 , wherein the distance of the electrical connection to the at least one of the end sections is between α eff and 3 α eff .