M. Dumitrescu

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.

High-speed resonant cavity light-emitting diodes at 650 nm

State-of-the-art resonant cavity light-emitting diodes (RC-LEDs) optimized for short-haul communication systems on polymethyl methacrylate (PMMA) plastic optical fiber (POF) are presented. The devices, emitting in the 650-nm wavelength range, are achieving, under different structure and working regime variants, high output power (15 mW), high external quantum efficiency (9.5%), record small-signal modulation bandwidth (f/sub -3/ /sub dB/ UP to 350 MHz), error free back-to-back transmission rates beyond 622 Mb/s, adjustable far-field pattern and good coupling efficiency into step index plastic optical fibers with reasonably large tolerances and without using auxiliary optics. The paper discusses the design concepts, modeling approaches, fabrication issues and performance characteristics of monolithic RC-LEDs emitting at 650 nm.

Nitrogen incorporation into GaInNAs lattice-matched to GaAs: The effects of growth temperature and thermal annealing

We have studied the effects of growth temperature and subsequent thermal annealing on nitrogen incorporation into lattice-matched dilute Ga0.942In0.058NAs-on-GaAs epilayers, which were grown by the molecular-beam epitaxy method. The samples were studied experimentally by means of x-ray diffraction and Raman spectroscopy and theoretically by calculations within the density-functional theory. Over the entire range of growth temperatures applied (410–470°C), nitrogen appeared to be mainly located on substitutional sites in “short-range-order clusters” as N–Ga4 and, to a lesser extent, as N–Ga3In. There were also indications of the presence of nitrogen dimers NN, as suggested by Raman spectroscopy, in qualitative agreement with the calculations. An increase in growth temperature reduced the amount of substitutional nitrogen and decreased the number of N–Ga4 clusters relative to N–Ga3In. Postgrowth thermal annealing promoted the formation of In–N bonds and caused a blueshift in the optical band gap, which incr...

Light-emitting diode emitting at 650 nm with 200-MHz small-signal modulation bandwidth

State-of-the-art modulation bandwidths are presented for multiquantum well resonant cavity light emitting diodes (RCLEDs) emitting at 650 nm. 84-/spl mu/m size epoxy coated RCLEDs have a 1.4-mW (CW) output power and a small signal modulation bandwidth of 200 MHz at 40 mA bias. 150-/spl mu/m diameter devices yield 3.25-mW and 150-MHz bandwidth at 70-mA bias. An open eye-diagram at 622 Mb/s achieved for the 84-/spl mu/m device makes it very attractive for SONET OC-12 data communication links.

Large array of single, site-controlled InAs quantum dots fabricated by UV-nanoimprint lithography and molecular beam epitaxy

We present the growth of single, site-controlled InAs quantum dots on GaAs templates using UV-nanoimprint lithography and molecular beam epitaxy. A large quantum dot array with a period of 1.5 µm was achieved. Single quantum dots were studied by steady-state and time-resolved micro-photoluminescence experiments. We obtained single exciton emission with a linewidth of 45 µeV. In time-resolved experiments, we observed decay times of about 670 ps. Our results underline the potential of nanoimprint lithography and molecular beam epitaxy to create large-scale, single quantum dot arrays.

SS-MBE-grown short red wavelength range AlGaInP laser structures

Short-wavelength GaInP/AlGaInP quantum-well (QW) laser diodes emitting in the 618-650 nm range at room temperature have been fabricated and characterized. Several variations in laser structures have been tested, including changes in QW composition, thickness, strain and number; changes in the barrier/waveguide composition and thickness; changes in cladding structure; use of multi-quantum-barriers and changes in the doping profile. The experiments showed that the threshold current characteristic temperature (T0) increases with the number of QWs and is higher for compressive strain. The use of graded-index (GRIN) waveguides and higher p-cladding doping induced both a reduction in threshold current density and an increase in T0, mostly at shorter wavelengths. Waveguide thickness optimization can be carried out, for both constant composition and GRIN waveguides, using the QW optical confinement as a first-approximation optimization criterion. Modified cladding structures reduced the vertical far-field full-width-at-half-maximum below 20° without significantly affecting the threshold current. Devices designed using some of the guidelines resulted from our study achieved, with different structures and under different operating conditions, performances like emitting more than 2W at 650 nm in continuous wave operation or lasing down to 618 nm at room temperature, which is among the shortest wavelengths from lasers grown by solid-source molecular-beam-epitaxy.

Influence of deep level impurities on modulation response of InGaP light emitting diodes

The effect of deep level impurities on static and dynamic properties of InGaP-based light emitters grown by all-solid-source molecular-beam epitaxy is analyzed. The improvement of the output power and the decrease in modulation bandwidth induced by the burn-in process are explained by the recombination enhanced annealing of one deep level trap. This assumption is experimentally proven through comparison of small-signal analysis for resonant cavity light-emitting diodes operating at 650 nm and deep level transient spectroscopy results. Finally, the concentration of the midgap recombination center N3 in the active region is shown to play an important role in the performance of the InGaP devices.