Bulent Cakmak

Aging of porous silicon and the origin of blue shift

Aging effects of porous silicon (PS) and the origin of blue shift are investigated. Photoluminescence (PL) measurements of the PS prepared with HF-EtOH solution showed a 210 meV blue shift after 1.5 months. It is found from deconvolution of the PL spectra that this shift is not fully related to the quantum confinement (QC) effect. For stable PS formation, a HFEtOH-H2O2 solution is used. A stable luminescence at 2.01 eV with a Gaussian distribution is obtained when the samples are kept in H2O2 for 45 min after the anodization.

Fabrication and characterization of dry and wet etched InGaAs/InGaAsP/InP long wavelength semiconductor lasers.

This paper presents fabrication and characterization of ridge waveguide InGaAs/InGaAsP/InP lasers with an operating wavelength of 1.5m using reactive ion etching (RIE), chemically assisted ion beam etching (CAIBE) and wet etching techniques. Characterization results of the lasers with 2m-wide waveguides are given of the two etching methods comparatively using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), L-I-V (Light-current-voltage) and spectral measurement techniques. Additionally, a comparison of wet and RIE etched lasers with 20m-wide waveguide is also discussed. Highly smooth (2.1+0.4nm rms surface roughness) and vertical (~90o) structures are obtained using RIE, in which the 2m-wide fabricated devices exhibit better performance over the CAIBE etched ones.

Surface diagnostics of dry etched III-V semiconductor samples using focused ion beam and secondary ion mass spectrometry

In order to optimize the H2/CH4 reactive ion etching process for InP, the surface composition of etched samples has been analyzed by means of a focused ion beam and secondary ion mass spectrometry. Harmful species of chlorine and oxygen have been identified as causing surface roughness and etch-rate fluctuations. Polymer distribution on the masked surface and etched surface phosphor abundance have been studied for various gas mixtures and rf power, establishing optimized CH4-rich etching conditions under which surface P content is closest to unetched material and polymer deposition is acceptable.

Scanning electron and atomic force microscopy measurements of ion beam etched InP samples using Ar/H2 chemistry

This paper reports scanning electron (SEM) and atomic force microscopy (AFM) results of ion beam (IBE) and chemically assisted ion-beam etched (CAIBE) InP wafers. While Argon (Ar) alone is used for the IBE process, the CAIBE is carried out by using Ar/H2/CH4 or Ar/H2 gases only. The evolution of the surface roughness and morphology is presented comparatively by varying acceleration voltage (Vacc), discharge current (Idis) and ion incidence angle. A drastic improvement of the surface roughness is obtained for the CAIBE using Ar/H2 chemistry and verified by atomic force microscopy measurements. The anisotropy of InP samples is also presented for two different masks; Al2O3 and Titanium (Ti) in the case of CAIBE mode. The most anisotropic structure of 83 degrees is performed by using the Ti mask. Finally, by using atomic force microscopy technique the lowest rms roughness of 4.3 is found in the case of using only Ar/H2 gasses.

High-power and picosecond pulse generation from a passively Q-switched tapered InGaAs/GaAs laser

Summary form only given. High-power picosecond optical pulses are required for a wide range of applications including optical switching, instrumentation, ranging, pumping, sensing, and spectroscopy. Q-switched pulses having an energy of 300 pJ and a duration of 40 ps were obtained from a 100-/spl mu/m-wide AlGaAs diode laser. However, widening the waveguide width generally results in a loss of spatial coherence. A majority of applications require both spatial and spectral coherence in the output optical pulse. Tapered waveguides have been used for enhancing pulse powers in Q-switched AlGaAs and InGaAsP (1.5 /spl mu/m) lasers. We report, for the first time to our knowledge, passively Q-switched pulses with 1.53 W peak power and 41 ps FWHM from an InGaAs/GaAs (970 nm) double-contact tapered semiconductor laser in a well defined single lobed far-field. We have fabricated the proposed two-section ridge-waveguide tapered device from an InGaAs/GaAs GRINSCH 2 QW wafer grown by MBE.

Smooth and anisotropic ion beam etching of InP with Ar/H2 chemistry

Ion beam etching (IBE) and chemically assisted ion-beam etching (CAIBE) of InP wafers are studied. While Argon alone is used for the IBE process, the CAIBE is carried out by using Ar/H2CH4. The realization of CAIBE in Ar/H2 atmosphere is also achieved for the first time. The evolution of the surface roughness and morphology is presented comparatively by varying acceleration voltage (Vacc), discharge current (Idis) and ion incidence angle. A drastic improvement of the surface roughness is obtained for the CAIBE using Ar/H2 chemistry. The etch rate of the InP structures is studied as a function of the Idis and the Vacc. A maximum etch rate of 700 angstrom/min is observed for 1.75kV acceleration voltage and 45 mA discharge current at 30 degrees ion incidence angle. The variation of the etch rate against the ion incidence angle is investigated both theoretically and experimentally. A good agreement between those is observed. Finally, the anisotropy of InP samples is presented for two different masks; Al2O3 and Titanium in the case of CAIBE mode. The most anisotropic structure of 83 degrees is performed by using the Ti mask.