Metamorphic InGaAs quantum well structures grown on GaAs reveal strong light emission at 1.3-1.6 mu m, smooth surface with an average roughness below 2 nm. and good rectifying I-V characteristics. Dark line defects are found in the QW Post growth thermal annealing further improves the luminescence efficiency but does not remove those dark line defects. Some challenges of epitaxial growth using this method for laser applications are discussed. (c) 2006 Elsevier B.V. All rights reserved.

We demonstrate 1.25–1.29μm metamorphic laser diodes grown on GaAs by molecular beam epitaxy (MBE) using an alloy-graded buffer layer (GBL). Use of Be in the GBL is effective to reduce surface/interface roughness and improves optical quality. The RMS surface roughness of the optimized metamorphic laser is only two atomic monolayers for 1×1μm2. Cross-sectional transmission electron microscopy (TEM) images confirm that most dislocations are blocked in the GBL. Ridge waveguide lasers with 4μm wide ridge were fabricated and characterized. The average threshold current under the pulsed excitation is in 170–200mA for a cavity length of 0.9–1.5mm. This value can be further reduced to about 100mA by high-reflectivity coating. Lasers can work in an ambient temperature up to at least 50°C.

We report molecular beam epitaxy (MBE) growth and device performance of 1.3μm GaInNAs/GaNAs single-quantum well lasers on GaAs substrates. Record low threshold current densities of 300, 320 and 360A/cm2 for cavity lengths of 1200, 1000 and 800μm, respectively, and a transparency current density of only 84A/cm2 are achieved for the 100μm wide broad area lasers. A characteristic temperature of 108K is measured in the temperature range of 8–70°C for a laser with a cavity length of 1000μm. We find that optimization of the RF nitrogen source during the MBE growth plays a crucial role in reducing the threshold current density.

The threshold and gain characteristics of GaInNAs single quantum well (QW) lasers with GaNAs and GaAs barriers, both emitting at 1300 nm, have been compared. The threshold current density for the laser with GaAs barriers is twice as high, presumably because of a higher monomolecular recombination rate caused by the higher N concentration in the QW. A significant difference in the spectral gain characteristics was also observed. Calculations show that this is due to a modification of the confinement potential for the conduction band electrons when incorporating N in the barriers and reducing the N concentration in the QW. An additional inhomogeneous broadening also had to be included in the calculations to obtain quantitative agreement between measured and calculated gain spectra.

We have studied theoretically the energy band structures and optical properties of highly strained dipole δ-doped In0.3Ga0.7As∕GaAs single quantum wells. Including dopant diffusion effect, strain in the quantum well, spin-orbital interactions, and many-body effects, the self-consistent calculations of the eight-band k∙p model and the Poisson equation show that the dipole δ doping induces an electric field across the In0.3Ga0.7As quantum well by the Stark effect so that both the interband transition energy and the wave-function overlap between the ground-state electrons and holes are reduced. Applying an external bias across the quantum well partially cancels the built-in electric field and reduces the wavelength redshift. The calculated material gain peak is close to the experimental lasing wavelength.

We demonstrate the wavelength extension of InGaAs/GaAs quantum well (QW) laser diodes (LD) by dipole /spl delta/-doping (DDD). This is achieved by introducing n- and p-type /spl delta/-doping close to each side of the QW, respectively. As a result, the internal electric field causes band bending which reduces the interband transition energy. Using this method, the lasing wavelength of an In/sub 0.36/Ga/sub 0.64/As/GaAs QW LD is shifted from 1.175 /spl mu/m to 1.206 /spl mu/m. Although electroluminescence shows that the lasing comes from electron and hole recombination in the excited states, we believe that this may provide a new method for long-wavelength InGaAs/GaAs QW laser fabrication.

We propose using dipole δ-doping across highly strained InGaAs/GaAs quantum wells (QWs) to achieve light emission at wavelengths in the range of 1.3–1.55 μm. For In0.3Ga0.7As/GaAs single QWs, we demonstrate that the photoluminescence (PL) wavelength increases with the doping concentration. With a transition energy reduction as large as 370 meV, PL emission at 1.548 μm at room temperature is realized. Broad area lasers with dipole δ-doping reveal longer lasing wavelengths than those of undoped lasers, although the wavelength redshift is much less than in the PL case.

High-quality 1.3 µm GaInNAs/GaNAs single quantum well lasers grown by molecular beam epitaxy are reported. The broad area lasers show a record low threshold current density of 318 A/cm2 for a cavity length of 1 mm, a transparent current density of 84 A/cm2, and a characteristic temperature of 103 K from 8 to 70°C.

We have studied the effect of different cap layers on optical property of InAs quantum dots (QDs) on GaAs (100) substrate. Temperature dependent photoluminescence (PL) indicates that the PL integrated Zn intensity from the ground state of InAs QDs capped with an intermediate InAlAs/InGaAs combined layer drops very little as compared to QDs capped with a thin InGaAs or GaAs layer from 15 K up to room temperature. PL integrated intensity ratio of the first excited to ground states for InAs QDs capped with an intermediate InAlAs/InGaAs layer is unexpectedly decreased with increasing temperature, which we tentatively attribute to phonon bottleneck effect.