Wataru Susaki

High-power 1.3-µm InGaAsP P-substrate buried crescent lasers

High performance of newly developed InGaAsP P-substrate buried crescent (PBC) laser diodes is described. It is shown that the PBC laser has superior characteristics to the conventional buried crescent (BC) laser with n-InP substrate. The maximum output power of 140 mW under a CW condition is realized at room temperature. CW light output power of 10 mW up to 110°C is achieved. A maximum CW temperature of 135°C is obtained. Stable CW operations have been confirmed in 70°C 5-mW and 70°C 20-mW aging tests. The reason for the high performance is discussed in relation to the leakage current which flows through the current blocking layers.

Acceptor Densities and Acceptor Levels in Undoped GaSb Determined by Free Carrier Concentration Spectroscopy

Without any assumptions regarding residual impurity species in an undoped semiconductor, it is experimentally demonstrated that the densities and energy levels of impurities can be precisely determined by the graphical peak analysis method based on Hall-effect measurements, referred to as free carrier concentration spectroscopy (FCCS). Using p-type undoped GaSb epilayers grown by molecular beam epitaxy (MBE), the densities and energy levels of several acceptor species are accurately determined. Five acceptor species are detected in the undoped GaSb epilayers grown by MBE, while two are also found in p-type undoped GaSb wafers. A 21–41 meV acceptor and a 75–99 meV acceptor exist both in the epilayers and in the wafer. On the other hand, a 164–181 meV acceptor is detected in epilayers grown at an Sb4/Ga flux beam equivalent pressure ratio of 8 or 10, while a 259 meV acceptor is found in the epilayer grown at Sb4/Ga = 6. In addition, a very shallow acceptor, which is completely ionized at 80 K, is found in the epilayers. The densities of the very shallow acceptor and the 21–41 meV acceptor are minimum at Sb4/Ga = 8, which makes the hole concentration lowest in the temperature range of the measurement.

Ten-thousand-hour operation of crank transverse-junction-stripe lasers grown by metal-organic chemical vapor deposition

For over 10 000 h, crank transverse-junction-stripe (TJS) laser diodes, grown by metal-organic chemical vapor deposition (MOCVD) maintain low and quite stable operating currents in the automatic-power-control aging with output power of 5 mW/facet at 55°C and 70°C. These MO-CVD lasers have excellent initial characteristics and small distributions of the characteristics. The reason for this excellent result is discussed in relation to the crystalline quality and the uniform growth of MO-CVD wafers.

High Temperature Single Mode CW Operation with a TJS Laser Using a Semi-Insulating GaAs Substrate

A new laser which has the simplest TJS structure on a semi-insulating GaAs substrate has been developed. Due to elimination of shunt current, the minimum threshold current has decreased to be as low as 12 mA. The temperature dependence of the threshold current has also much improved. The new laser mounted upside up operates continuously up to 110°C in a single longitudinal and fundamental transverse mode. The estimated lifetime of the lasers is more than 105 hours at 25°C.

Internal loss of InGaAsP/InP buried crescent (λ = 1.3 μm) laser

The temperature dependence of the internal loss α of the InGaAsP/InP buried crescent laser is presented in the temperature range 20–80 °C. α is about 18 cm−1, and no apparent temperature dependence of α is observed in this temperature range. This indicates that the temperature‐sensitive behavior of the threshold current in InGaAsP/InP long‐wavelength lasers is not due to the temperature dependence of internal loss. The decrease in the external quantum efficiency with increasing temperature is attributed to the decrease in the internal quantum efficiency.

Carrier confinement in strain-compensated InGaAs/GaAsP quantum well laser with temperature-insensitive threshold

Temperature insensitive threshold current in strain- compensated-(InxGa1-xAs/GaAsP) SQW-lasers with x X 0.3 is investigated by changing x equals 0.2, 0.25 and 0.3 by the spectral measurement and the threshold carrier density determined by lasing delay. Large energy separation between the heavy and the light hole subbands due to the highly compressive strain makes it not to exist the light hole subbands in the quantum well, which is confirmed by the induced Raman scattering spectral above threshold. Injected holds are almost contained in the heavy hole subbands, and injected electrons are also contained in the electron subbands at threshold in these lasers at room temperature.

Study on droop characteristics of laser diodes as light sources of laser beam printer

To obtain a small droop, which is the ratio of transient reduction of output power after the laser diode (LD) is turned on, the influence of quantum efficiency and transient thermal flow of laser diodes is investigated both theoretically and experimentally. The analysis shows that as the thermal resistance between active region and heatsink is decreased and the reflectivity of front facet is increased, the droop decreases. The results are applied to self-aligned structures with bent active layer laser diodes (SBA LDs). By employing a junction-down configuration for assembly of the SBA laser chips and silicon carbide (SiC) as a submount material, and by coating the front facet so as to have reflectivity of 50% with taking into reduction of catastrophic optical damage (COD) level, the droop is decreased to 7.0%. In contrast, in the conventional SBA LDs which have a junction-up configuration with silicon (Si) as the submount material and have only a passivation coating on the front facet, value of the droop is 17.5%. Our results serve as a guide to the design of the light source of laser beam printers (LBPs).

Influence of Oxygen in Ambient Gas on LPE GaAs Layers

The influence of oxygen in ambient gas on liquid phase epitaxial GaAs layers is investigated. The oxygen concentration in the ambient gas during liquid phase epitaxial growth is quantitatively measured. The carrier concentration increases from 1×1015 cm-3 to 2.5×1017 cm-3 in proportion to the oxygen concentration in the ambient gas. The saucer pit density produced by molten KOH etchant and the relative emission intensity of photoluminescence spectra due to deep levels drastically decrease in the undoped GaAs layers grown under the oxygen concentration less than 0.03 ppm. The density of dark spot defects is also reduced to a few hundred per square centimeter in the Si-doped GaAs layers grown on Te-doped GaAlAs layers under the oxygen concentration less than 0.03 ppm. The oxygen incorporated into grown layers seems to be related with the formation of those defects.

Hign-Power Long-Cavity T3 Laser with a Very Narrow Beam

A 790 nm AlGaAs laser with a thin tapered thickness active layer (T3 laser), whose cavity length is 350 µm, has been developed. As the beam divergence of the laser becomes narrower, the threshold current does not increase. Both the current density and the thermal resistance can be reduced by extending the cavity length of the laser. The laser emitted a light output power over 100 mW even at 80°C and proved to have a fundamental transverse mode at least up to 120 mW. The stable 50 mW operation at 50°C over 2000 hours has been confirmed.

Low Threshold Current 1.3 µm InGaAsP Buried Crescent Lasers

The threshold current and beamwidth of the fundamental transverse mode have been examined of the buried crescent (BC) laser. The active region with less than 2.0 µm wide was successfully grown inside the channel prepared on the InP substate and the minimum threshold current of 8 mA has been obtained at room temperature (cavity length L=300 µm). An analytical expression for the beamwidth of far field patterns parallel to the junction plane (θ//) has been obtained and it was confirmed that a good agreement is shown between the theoreitcal calculation and the experimental result.