Hong Man Kim

High-Performance Strain-Compensated Multiple Quantum Well Planar Buried Heterostructure Laser Diodes with Low Leakage Current

The dependence of leakage current in a planar buried heterostructure laser diode (PBH-LD) on the operating temperature was analyzed by taking the effects of the connection width between a p-InP clad layer and a p-InP blocking layer into account. A two-step etching process comprising nonselective mesa etching followed by InP selective etching is proposed for obtaining a narrow connection width and high controllability of an active layer width. The performance was compared for LDs fabricated using the two-step etching process and those fabricated using conventional nonselective etching process. The average threshold current and the slope efficiency of the 1.3 µ m strain-compensated multiple quamtum well (MQW) PBH-LD fabricated using the two-step etching process were 5.6 mA and 0.27 mW/mA, respectively, for a cavity length of 400 µ m. However, using the nonselective etching process, the average threshold current was 14.5 mA and the slope efficiency was 0.22 mW/mA, given the same cavity length. A higher differential gain and characteristic temperature were also obtained due to the lower leakage currents and strain-compensated multiple quantum well active layers.

InAsP phase formations during the growth of a GalnAsP/lnP distributed feedback laser diode structure on corrugated lnP using metalorganic vapor phase epitaxy

An InAsP phase formed during the heatup time to the growth temperature of MOVPE was investigated by transmission electron microscopy and energy dispersive spectroscopy. The thickness of the InAsP phase on the concave regions of corrugation is increased with increased AsH3 partial pressure and heat‐up time. The arsenic composition in InAsP was also increased with the increase of AsH3 partial pressure during the heat‐up time. Dislocations and defects were not generated below an AsH3 partial pressure of 2.4×10−3 Torr, although strain was induced according to the thickness and composition of InAsP formed on the concave regions of corrugation.

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.

Uniform and high coupling efficiency between InGaAsP-InP buried heterostructure optical amplifier and monolithically butt-coupled waveguide using reactive ion etching

We obtained uniform and high coupling efficiency for InGaAsP-InP buried heterostructure (BH) optical amplifiers integrated with butt-coupled waveguides using reactive ion etching (RIE) for mesa definition and low-pressure metalorganic vapor phase epitaxy (LPMOVPE) for waveguide layer regrowth. Measured average coupling efficiency was over 91% across a quarter of 2-in InP wafer. RIE etched vertical facet and a subsequent chemical etching using HBr-based solution for relief of RIE damage enabled us to reduce the coupling loss due to anomalous regrowth shape at the interface. RIE and selective regrowth processes are promising techniques for the fabrication of the photonic integrated circuit (PIC).

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.

COMPARISON OF FE- AND P/N/P-DOPED INP AS A CURRENT BLOCKING LAYER FOR MONOLITHICALLY INTEGRATED INGAASP/INP LASER DIODES WITH PASSIVE WAVEGUIDES

We have fabricated InGaAsP/InP waveguide integrated laser diodes for the 1550 nm wavelength region. The passive waveguide was butt-coupled using the CH4/H2 reactive ion etching and metal-organic chemical vapor deposition regrowth techniques. We compared the performances of waveguide integrated laser diodes with different current blocking layers, i.e., Fe-doped InP and p/n/p-doped InP layers. On the whole, Fe-doped InP was better than p/n/p-doped InP as a current blocking layer. In particular, the reverse leakage current through the butt-coupling region with Fe-InP current blocking layer was approximately 99.9 µA, while that with p/n/p-InP was 193.7 µA. We also discussed the leakage current characteristics of waveguide integrated laser diodes with analyses of IdV/dI vs I curves.

Effects of heat-up procedure and grating depth on the erosion of InGaAs grating

Abstract Effects of heat-up procedure and grating depth on the erosion of InGaAs absorptive layers and the quality of strained multiple quantum wells (MQWs) were investigated using transmission electron microscopy (TEM) and double crystal X-ray diffraction (DXRD) analysis, in the fabrication of loss-coupled distributed feedback laser diodes (DFB-LDs) that have absorptive grating on the side of substrate. Decomposition of an InGaAs grating depends on the growth starting temperature and grating depth. Even before starting InP growth, a part of the InGaAs was decomposed during the heat-up process. These decomposed adatoms of indium, gallium, and arsenic seem to migrate to the concave region of the grating and then form a new material phase at the bottom of the concave region. At the initial stage of InP planarization layer growth, InP growth on the InGaAs mesa does not take place until the concave region of grating is fully filled, while a part of InGaAs is decomposed. Desorbed adatoms seemed to migrate to the upper part of the growing InP on the concave region and form another new material phase in this region. The growth technique of n-InP planarization layers over shallow gratings with the growth starting temperature of 550°C allows strained MQWs of good crystalline quality, leading to the successful fabrication of very low threshold loss-coupled DFB-LDs.

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.

Interfacial layer formation on corrugated InP during the epitaxial growth of GaInAsP InP distributed feedback laser diode structure

Abstract The interfacial layer formed during the soaking procedure of liquid phase epitaxy (LPE) growth and the heat-up procedure to the growth temperature of metalorganic vapor phase epitaxy (MOVPE) was investigated by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). A thin interfacial layer between an epitaxially grown GaInAsP layer and the concave region of the corrugated InP grating is formed in LPE growth using a GaAs cover crystal. The thickness of this interfacial InAsP layer in the concave region of corrugation is increased with increased AsH 3 partial pressure and heat-up time in MOVPE. The arsenic composition in the InAsP layer also increased with increased AsH 3 partial pressure. Dislocations and defects were not generated in LPE growth using a GaAs cover crystal and using an AsH 3 over pressure and heat-up procedure to the growth temperature in MOVPE.