H.S. Djie

Experimental and theoretical analysis of argon plasma-enhanced quantum-well intermixing

Plasma-enhanced quantum-well intermixing (QWI) has been developed for tuning the bandgap of InGaAs-InP material using an inductively coupled plasma system. The application of inductively coupled plasma enhances the interdiffusion of point defects resulting in a higher degree of intermixing. Based on a semi-empirical model of QW interdiffusion, the bandgap blue-shift with respect to the plasma exposure time and inductively coupled plasma energy has been analyzed. The theoretical results appear to be in good agreement with the experimental data of the intermixed samples. The model serves as a good simulation tool to explain the intermixing mechanism and further to optimize the intermixing process for the fabrication of the photonic integrated circuits.

Plasma-induced quantum well intermixing for monolithic photonic integration

Plasma-induced quantum well intermixing (QWI) has been developed for tuning the bandgap of III-V compound semiconductor materials using an inductively coupled plasma system at the postgrowth level. In this paper, we present the capability of the technique for a high-density photonic integration process, which offers three aspects of investigation: 1) universality to a wide range of III-V compound material systems covering the wavelength range from 700 to 1600 nm; 2) spatial resolution of the process; and 3) single-step multiple bandgap creation. To verify the monolithic integration capability, a simple photonic integrated chip has been fabricated using Ar plasma-induced QWI in the form of a two-section extended cavity laser diode, where an active laser is integrated with an intermixed low-loss waveguide.

Wavelength monitoring with low-contrast multimode interference waveguide

We demonstrate a wavelength monitor based on interference effect in planar quantum-well waveguide fabricated using argon plasma quantum-well intermixing. The passive device exhibits a characteristic curve, which is used to determine the wavelength of an arbitrary input light near the 1550-nm window. It has an exponential-like wavelength response in the wavelength range 1520-1620 nm and resolution of 0.2 nm.

Large blueshift in InGaAs/InGaAsP laser structure using inductively coupled argon plasma-enhanced quantum well intermixing

An inductively coupled plasma-enhanced quantum well intermixing technique has been developed to induce a shift in the band gap in quantum well structures using argon plasma. The emission of the InGaAs/InGaAsP laser structure was blueshifted as much as 104 nm with linewidth broadening of only 10.6 nm using 5 min plasma exposure and subsequent rapid thermal annealing. This large shift is attributed to inductively coupled plasma at high ion current density (with 100’s of eV ion impact energy) that promotes desirable point defects near the surface of the samples. The result has demonstrated an effective approach for large band gap tuning of InGaAs/InGaAsP laser structures.

Photoluminescence enhancement by inductively coupled argon plasma exposure for quantum-well intermixing

The exposure of InGaAs/InGaAsP quantum-well (QW) structures to argon (Ar) plasma in an inductively coupled system has been studied. An increase in photoluminescence (PL) intensity without PL peak shift was observed for 5-min Ar plasma exposure compared to the as-grown sample. The exposure creates point defects, and upon rapid thermal annealing produces intermixing between barriers and QWs, resulting in the blueshift of QWs. A selective intermixing using a 200-nm-thick of SiO2 layer as an intermixing mask exhibited a differential band-gap blueshift of 86 nm, with a differential linewidth broadening of 0.3 nm between masked and unmasked section. The improvement of PL intensity in combination with selective intermixing process can pave the way for high-quality hybrid photonic and optoelectronic integrated circuits.

Thermally induced diffusion in GaInNAs∕GaAs and GaInAs∕GaAs quantum wells grown by solid source molecular beam epitaxy

The effects of the thermal annealing induced diffusion on the photoluminescence (PL) of a GaAs∕GaInAs∕GaAs∕GaInNAs∕GaAs quantum well (QW) structure grown by solid source molecular beam epitaxy are studied. The PL experimental results in conjunction with the numerical quantum-mechanical modeling that predicts the changes in the QW confining potential with group-III atomic diffusion, have been used to obtain the values for diffusion coefficient. The activation energies of GaInAs∕GaAs QW (ED,GIA) were found to be between 0.49to0.51eV, while that of GaInNAs∕GaAs QW (ED,GINA) showed comparable values of between 0.6 to a 0.67eV, as annealing time increases from 10to30s. The ED,GIA and ED,GINA values are attributed to the same interstitial diffusion mechanism.

Single step quantum well intermixing with multiple band gap control for III-V compound semiconductors

We report a quantum well intermixing technique based on Ar plasma induced damage on both GaAs- and InP-based materials with single-step multiple band gap creation across a substrate. A quantum well structure with multiplewidths serves as a sensitive tool to probe the damage created by Ar plasma. The analysis reveals that the surface defects were created up to a certain depth and propagated deeper into the material upon subsequent annealing. A simple and reliable way to obtain a controlled multiple band gap was achieved by using the spatial defect modulated intermixing. Eight band gap levels were realized across a single chip of quantum well laser structure with a linear relationship to the fraction of the open area under plasma exposure. This simple approach can be implemented at a postgrowth level to a wide range of material systems to achieve multiple band gaps, suitable for photonic integration.

Implementing multiple band gaps using inductively coupled argon plasma enhanced quantum well intermixing

The implementation of multiple band gaps on a single InP substrate with an InGaAs∕InGaAsP quantum well laser structure via the control of local defect concentrations in the process of inductively coupled argon (Ar) plasma enhanced quantum well intermixing is reported. With multistep plasma exposure, different levels of near-surface point defect concentrations are established in different areas, which lead to different extents of band gap modification in a single-step rapid thermal annealing (RTA). Three distinct band gaps with blueshifts of 84, 66, and 3nm with respect to that of the as-grown sample are achieved in a process involving two steps of Ar plasma exposure and a single step of annealing in nitrogen ambient at 600°C for 2min. As an indication of material quality preservation, no intensity reduction and linewidth broadening in the photoluminescence caused by the process has been observed. This work demonstrates a practical approach of multiple band gap modification for the InP-based photonic integ...

Passive wavelength monitor based on multimode interference waveguide

A new wavelength monitor based on a multimode interference waveguide is proposed for multiwavelength communication applications. The device characteristics are studied using the beam propagation method. By adjusting the waveguides geometric length, different wavelength ranges can be addressed. Each device can monitor up to a 50-nm range and has accuracy <5 A.

Analysis and modeling of distributed feedback and distributed Bragg reflector lasers using regrowth-free index-coupled surface grating technology

The modeling of single-mode distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers based on an index-coupled sur- face grating on the InGaAs/InGaAsP multiple-quantum-well (MQW) structures is carried out. Such lasers require relatively simpler grating fabrication processes without multistep-epitaxial growth or regrowth, as required in conventional devices. A key concern for surface grating is designing structure that can provide sufficient feedback to achieve single-mode operation and high laser performance. Bragg wavelength operation of the surface grating (SG) DFB and SG DBR lasers can be satisfied by etching deep and fine gratings on the surface of both side portions and along the top of the ridge stripe, respectively. The numerical results obtained enable optimization of grating and laser geometries to provide the desired feedback effect. The simulated laser design shows that single-frequency operation at a wavelength of 1.55 mm with high a side-mode suppression ratio (SMSR) is attainable.