E.-M. Pavelescu

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.

Photoreflectance evidence of multiple band gaps in dilute GaInNAs layers lattice-matched to GaAs

Dilute Ga1−xInxNyAs1−y∕GaAs quantum wells with high In-content, which are under compressive strain, have been shown previously to exhibit multiple band gaps, likely due to the presence of different nitrogen nearest-neighbor environments, i.e., N‐Ga4−mInm(0⩽m⩽4) short-range-order clusters. Here, photoreflectance (PR) measurements on lattice-matched dilute GaInNAs-on-GaAs layers with low indium and nitrogen content are reported, which give evidence that these layers also exhibit several distinct band gaps. These distinct band gaps, which were found to coexist, are associated with different nitrogen bonding configurations, as revealed by Raman spectroscopy. Thus, the metastable nature of GaInNAs seems to be a persistent intrinsic property, irrespective of strain and indium content. The annealing-induced blueshift of GaInNAs band gap energy, which is usually observed in this system, has been associated with the change in the intensity of PR resonances related to different N‐Ga4−mInm configurations.

Growth-temperature-dependent (self-)annealing-induced blueshift of photoluminescence from 1.3 μm GaInNAs/GaAs quantum wells

Growing the capping layer of a GaInNAs/GaAs quantum well at typical substrate temperature for GaAs growth by molecular-beam epitaxy, like 580 °C, was found to induce a blueshift of the quantum-well emission whose magnitude significantly increased as the quantum-well growth temperature was decreased. The growth-temperature-dependent (self-)annealing-induced blueshift is correlated with the presence of indium and occurs without observable changes in alloy macroscopic composition or quantum-well structure. The underlying cause for the increase in blue shift with decreasing quantum-well growth temperature appears to be an enhancement in the amount of In–N bonds formed by (self-)annealing, likely through a defect-assisted mechanism.

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.

The energy-fine structure of GaInNAs∕GaAs multiple quantum wells grown at different temperatures and postgrown annealed

We report photoreflectance investigations of the energy-fine structure of GaInNAs∕GaAs multiple quantum wells (MQWs) grown at different temperatures and postgrown treated by rapid thermal annealing (RTA). A “splitting” of the ground and excited QW transitious due to the presence of different nitrogen nearest-neighbor environments, i.e., N‐Ga4−mInm(0⩽m⩽4) short-range-order clusters, has been observed. The RTA induces a nitrogen redistribution between the five possible N‐Ga4−mInm configurations and thus leads to a blueshift of QW transitions. The magnitude of the blueshift and its dependence on the growth temperature and annealing temperature are investigated in this paper.

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...

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.

Electron-irradiation enhanced photoluminescence from GaInNAs∕GaAs quantum wells subject to thermal annealing

Electron irradiation of a 1.3‐μm‐GaInNAs∕GaAs multi-quantum-well heterostructure, grown by molecular beam epitaxy and subsequently rapid-thermal annealed, is found to induce much stronger photoluminescence than what is observed for an identical as-grown sample upon annealing. Annealing of the irradiated sample also causes a small additional spectral blueshift and reduces alloy potential energy fluctuations at the conduction band minimum. These irradiation-related phenomena are accompanied by small but discernable changes in x-ray diffraction features upon annealing, which indicate compositional and∕or structural changes in the quantum wells.