Hyung Mun Kim

Improvement of linewidth enhancement factor in 1.55-μm multiple-quantum-well laser diodes

The improvement of the linewidth enhancement factor in complex-coupled laser diode (CC-LD), or loss-coupled, was confirmed by measuring the spontaneous emission spectra below threshold from the sidewall of laser diodes. In addition, the serial resistance of the device was measured. The linewidth enhancement factor is improved by the presence of a light absorbing InGaAs grating for loss coupled distributed-feedback (DFB) laser diode (LD). We report the comparison of the linewidth enhancement factors of Fabry-Perot (FP) LD, conventional DFB-LD, and loss coupled DFB-LDs.

Fabrication of InP-Based Reflection Type Arrayed Waveguide Grating with Metal Coated Reflection Facet

We have fabricated a reflection type arrayed waveguide grating that consists of one free propagation region and arrayed waveguides which are all strainght waveguides. Each arrayed waveguide has a reflection facet formed by lithography. All reflection facets were coated with metal for high reflection. The device is an 1×8 multi/demultiplexer with 1.6 nm channel spacing. The chip size is as small as 0.83 ×2.7 mm2. The on-chip loss is about -13 dB and the crosstalk is less than -13 dB.

Cavity length dependence of high-speed 1.55-μm multiple-quantum-well laser diode characteristics

Spontaneous emission spectra below threshold were measured from the side wall of InGaAs QW laser diodes to extract laser design parameters such as cavity length dependence of gain, linewidth enhancement factor, and serial resistance. The threshold current varies according to the change of cavity length, and thus, the lasing peak shifts and the serial resistance changes. It is interesting that the linewidth enhancement factor, however, is not deteriorated by shortening cavity length. The short cavity length would rather improve the linewidth enhancement factor mainly by shifting the lasing peak to smaller wavelength side, where the linewidth enhancement factor is inherently low.

The contraction of lattice constant and the reduction of growth rate in p-InGaAs grown by organometallic vapor phase epitaxy

We have investigated the effect of diethylzinc (DEZn) on the lattice constant and the growth rate of InGaAs. Introducing DEZn for p-type doping induces the contraction of lattice constant and the reduction of growth rate compared to undoped InGaAs. Depletion of indium is responsible for these effects. These effects are reduced at lower growth temperatures or at lower growth pressures. From the observed effects of the growth temperatures and the growth pressures on the contraction of the lattice constant, it is concluded that depletion of indium occurs in the gas phase.

The effect of strain on the dielectric constants of strained In0.7Ga0.3AsyP1−y films

We measured the dielectric constants of strained In0.7Ga0.3AsyP1−y (y=0.2, 0.4, 0.8, 1.0) and lattice-matched 1.32 μm In1−xGaxAsyP1−y thin films grown on InP substrates by metalorganic chemical vapor deposition. Measurements were performed by phase-modulated spectroscopic ellipsometry in the range of 0.76–4.9 eV. Our data bridge the gap between literature data in the near-infrared region and those in the visible-ultraviolet region. The critical point energies of strained In0.7Ga0.3AsyP1−y were compared with unstrained counterparts and were found to be shifted in accordance with the theory, which predicts that the compositional shift is compensated. Thus, the critical point energies of strained In1−xGaxAsyP1−y thin films of arbitrary composition can be estimated accurately and, conversely, the composition of strained In1−xGaxAsyP1−y thin films can be estimated by measuring their critical point energies, as for unstrained materials.

Highly reproducible methods for fabrication of InP reflective arrayed waveguide grating demultiplexer

We have designed and fabricated a reflective type of InP-based arrayed waveguide grating demultiplexer using highly reproducible and novel methods, such as lithography, metal coating for high reflection, and lift-off, not cleaving a chip in half.

Structural and device properties of DFB-LD with lateral undulation of SL-MQW

The InGaAsP/InGaAs strained-layer multiple quantum well (SL-MQW) structures for 1.3 /spl mu/m or 1.55 /spl mu/m distributed feedback laser diodes (DFB-LD) have been grown by low-pressure metalorganic vapor phase epitaxy. We observed the lateral undulation or deformation of SL-MQW grown on sawtooth-patterned substrates before the fabrication of DFB-LD, and it was dependent upon the initial growth conditions, AsH/sub 3/ partial pressure and heat-up time, prior to the 1st active layer growth. It is mainly due to the excess accumulation of strain in a given growth condition. The structural qualities of SL-MQW are analyzed in-depth using DCXRC, PL, TEM, SEM, and OM. We will discuss the effect of undulation or deformation on the device properties, such as I-V, I-L, differential quantum efficiency, internal loss, and characteristic temperature.

SCH dependence of linewidth enhancement factor for high-speed 1.55-μm multiple quantum well laser diodes

The linewidth enhancement factor is the crucial design parameter with others, such as gain and refractive index changes for semiconductor laser diodes (LD). The changes of characteristics are measured according to the variation of the thickness of SCH (Separate Confinement Heterostructure, 1.24 micrometer p-InGaAsP). The gain spectra were obtained from the spontaneous emission for three LDs. The threshold current; Ith were about 15 mA. The optical field profiles for various SCH thickness was calculated from the effective index and transfer matrix method and the corresponding optical confinement factors are compared with the variation of measured (alpha) . It is meaningful to find the SCH thickness, SCH(Gamma max), of maximum confinement (Gamma) for given LD structure. Although the improvement of the linewidth enhancement factor ((alpha) ) in thicker SCH (greater than SCH(Gamma max)) has been known, it has not been measured for thin SCH (less than SCH(Gamma max)). Here, we compare the measured linewidth enhancement factors of three DFB-LDs with different SCH thickness of 500, 750, and 1000 angstrom, which are all smaller than the SCH(Gamma max) for given structure. It is shown that (alpha) would be improved as SCH thickness increases up to 1500 angstrom (approximately SCH(Gamma max)) for given structure if other design parameters permit.

Optimization of growth conditions for the OMVPE grown InAsP/InP quantum well

We have investigated the optical quality of a InAsP/InP single quantum well with a 40 /spl Aring/ well thickness grown by organo metallic vapor phase epitaxy at various growth conditions such as growth temperature, V/III ratio, and growth rate, using room temperature photoluminescence (PL) and high resolution X-ray diffraction. The full width at half maximum of PL peaks always increases with the increase of As composition regardless of the growth conditions. However, we observe several different behaviors of PL peak broadening depending on the growth conditions. This different behavior is well described as a function of AsH/sub 3/ flow rate. Based upon our results, we suggest that relatively low growth temperature and low V/III ratio are suitable for the growth of high quality InAsP/InP quantum well structure.

A new fabrication method of micro-grating and its application to long wavelength distributed feedback laser diode

Summary form only given. Tne fabrication technology of the first order InP grating has been one of the important steps to make long wavelength distributed feedback [DFB] laser diodes. In this paper, the rectangular grating is fabricated from an intermediate SiN/sub x/ layer on InP substrate by using the conventional holographic exposure and RIE. To our knowledge, our process is the first report that SiN/sub x/ layer is utilized not only as the image transferred layer from photoresist layer but also as the mask layer for InP dry etching.