C.S. Peng

Low-threshold-current 1.32-μm GaInNAs/GaAs single-quantum-well lasers grown by molecular-beam epitaxy

Using solid-source molecular-beam epitaxy with a rf-plasma source, we have grown GaInNAs/GaAs single-quantum-well lasers operating at 1.32 μm. For a broad-area oxide stripe, uncoated Fabry–Perot laser with a cavity length of 1600 μm, the threshold current density is 546 A/cm2 at room temperature. The internal quantum efficiency for these lasers is 80%, while the materials losses are 7.0 cm−1. A characteristic temperature of 104 K was measured in the temperature range from 20 to 80 °C. Optical output up to 40 mW per facet under continuous-wave operation was achieved for these uncoated lasers at room temperature.

Effects of insertion of strain-mediating layers on luminescence properties of 1.3-μm GaInNAs/GaNAs/GaAs quantum-well structures

We present a 1.3-μm GaInNAs/GaAs quantum-well heterostructure, which consists of a strain-mediating GaInNAs layer grown between a compressive-strained quantum well and a tensile-strained GaNAs layer. Compared to a similar sample with no strain-mediating layer, this heterostructure exhibits improved material properties and remarkable redshift of emission with enhanced light intensity. The observations are based on photoluminescence spectra and x-ray diffraction data measured for the active region of the samples.

1.32-μm GaInNAs-GaAs laser with a low threshold current density

In this letter, we report on a recent development of diluted nitride laser diodes operating at the wavelengths around 1.3 /spl mu/m. The lasers grown by molecular beam epitaxy and processed into 20-/spl mu/m-wide ridge waveguide structures, mounted episides up on subcarriers, exhibit a threshold current density as low as 563 A/cm/sup 2/, slope efficiency of 0.2 W/A per facet, light power up to 40-mW continuous-wave, and characteristic temperature of 97-133 K.

Suppression of interfacial atomic diffusion in InGaNAs/GaAs heterostructures grown by molecular-beam epitaxy

We have studied the effects of annealing of InGaNAs/GaAs heterostructures on diffusion at the interfaces and the resultant changes in optical and structural properties. Interdiffusion between In and Ga was found to be very significant. Inserting a thin compressively strained layer of InxdGa1−xdNydAs1−yd on either side of an InxqGa1−xqNyqAs1−yq quantum well (QW) suppressed this interdiffusion significantly. As a consequence, a blue shift of the photoluminescence signal after annealing remained small and the optical activity was largely improved. It was also found that a small amount of N incorporated in InGaAs QWs embedded in GaAs increased the In/Ga interdiffusion and that increased mechanical stresses enhanced the interdiffusion.

Strain-compensated GaInNAs structures for 1.3-/spl mu/m lasers

GaAs-based dilute nitride lasers are potential light sources for future optical fiber communication systems at the wavelength of 1.3 /spl mu/m. In this paper we discuss the results of studies of optimization of the growth conditions and active regions of the GaAs-based lasers. To this end, a series of samples were grown using the molecular beam epitaxy technique. The active regions consisted of quantum wells, strain-compensating layers, and strain-mediating layers. They were characterized by photoluminescence and double crystal X-ray diffraction methods. The optical properties were very much affected by a choice of growth conditions, details of the quantum wells, and postgrowth thermal treatment. Preliminary results on diode-pumped vertical-cavity surface emitting lasers, which launch light power of 3.5 mW coupled into a single-mode fiber, are also presented.

Annealing effects on optical and structural properties of 1.3-μm GaInNAs/GaAs quantum-well samples capped with dielectric layers

Effects of thermal annealing on photoluminescence (PL) and x-ray diffraction from metastable GaInNAs/GaAs quantum-well samples covered by dielectric layers have been studied. PL from uncoated samples exhibits a saturable blueshift of 22 meV relative to PL from the as-grown samples in these experiments. The shift is attributable to a change in the nearest neighbors of nitrogen in short-range-order N-InmGa4−m (0⩽m⩽4) clusters at a fixed composition with negligible Ga/In/N interdiffusion. A Si3N4 cap layer effectively prevents the blueshift in the early stage of annealing and improves emission intensity. Under severe annealing conditions (750 °C for 1500 s), the maximum blueshift for the Si3N4-covered samples is 31 meV. A SiO2 cap layer causes a large nonsaturable blueshift, almost 100 meV in these experiments. The large blueshift is assigned to the formation of defects (likely Ga vacancies) at the SiO2/GaAs interface. The defects are believed to diffuse into the bulk at elevated temperatures and to assist G...

Postgrowth annealing of GaInAs∕GaAs and GaInAsN∕GaAs quantum well samples placed in a proximity GaAs box: A simple method to improve the crystalline quality

The effects of thermal annealing on GaInAs∕GaAs and GaInAsN∕GaAs quantum wells, grown by molecular beam epitaxy, were investigated. Optical and structural properties were examined upon annealing when the samples had a 200nm thick SiO2 cap layer, or were placed in a so-called GaAs box or were left uncapped. The GaAs box gave rise to the strongest photoluminescence without significant blueshift or structural changes at moderate annealing temperature. Capping with SiO2 impaired the samples and caused a more pronounced blueshift for the GaInAs quantum wells than for the GaInAsN ones. These results consolidate our understanding of the blueshift mechanisms.

Enhanced optical performances of strain-compensated 1.3-μm GaInNAs/GaNAs/GaAs quantum-well structures

We report on luminescence properties of GaInNAs/GaNAs/GaAs quantum-well structures emitting light at the wavelength of 1.3 μm, grown by molecular beam epitaxy. The design of the structure consists of a strain-mediating GaInNAs layer, sandwiched between a highly compressive GaInNAs quantum well and a strain-compensating GaNAs layer. Insertion of the strain-mediating layer improves optical activity of the quantum well and shifts the spectrum to longer wavelengths.

Annealing of self-assembled InAs/GaAs quantum dots: A stabilizing effect of beryllium doping

We investigated the effects of postgrowth thermal annealing on optical properties of beryllium-doped InAs quantum dot (QD) heterostructures grown by molecular beam epitaxy. Thermal annealing induced a blueshift of up to 200 meV in light emission from an undoped sample, while a sample having GaAs layer heavily doped with beryllium on top of the QD region exhibited a much smaller blueshift. This phenomenon is interpreted as due to suppression of annealing-induced In/Ga interdiffusion.

Suppression of annealing-induced In diffusion in Be-doped GaInAsN/GaAs quantum well

The authors report on an interesting observation regarding thermal annealing of a beryllium-doped Ga0.65In0.35As0.99N0.01/GaAs quantum well (QW) grown by molecular beam epitaxy. A QW doped at 6×1019 cm−3 exhibited superior thermal properties and about six times larger photoluminescence than an undoped QW of the same structure. X-ray diffraction and secondary ion mass spectrometry provided evidence that beryllium suppressed indium diffusion and stabilized (metastable) dilute nitride heterostructure upon annealing.