G. Coudenys

Monolithic integration of a spot size transformer with a planar buried heterostructure InGaAsP/InP-laser using the shadow masked growth technique

We present a vertically tapered InGaAsP/InP planar buried heterostructure (PBB) laser for low loss coupling to single-mode fibers. To achieve the vertical tapering we make use of the shadow masked growth technique. Tapered lasers with beam divergences of 15/spl deg/ in both lateral and transverse directions were realized. In comparison with untapered lasers, the coupling losses to cleaved single-mode fibers could be reduced by 4.8 dB down to 5.8 dB.<<ETX>>

III-V semiconductor waveguiding devices using adiabatic tapers

Abstract In the past few years much effort has been put into the fabrication and optimization of III–V semiconductor waveguiding devices with integrated adiabatic mode size converters (tapers). By integrating a taper with a waveguide device, one wants to reduce the coupling losses and the packaging cost of OEICs in future optical communication systems. This paper gives an overview of different taper designs, their performance and the technological approaches used in realizing such tapered devices.

Relaxed lattice-mismatched growth of III–V semiconductors

Abstract The fast increase in complexity of electronic and optoelectronic systems has created a need for high performance and multifunctional integrated circuits. One of the major restrictions is the lattice matching condition which severely limits the number of possible material combinations that can be used. This paper will review recent developments in the relaxed combination of III–V semiconductors with lattice mismatched substrates. Emphasis will be put on the problems encountered, the possible solutions and the device applications. The material combinations which will be discussed are: GaAs/AlGaAs on Si and InP substrates and InP/InGaAsP on Si and GaAs substrates.

Influence of gas mixing on the lateral uniformity in horizontal MOVPE reactors

Abstract Two novel gas mixing devices, which can be easily implemented in a horizontal MOVPE reactor, have been designed in order to achieve better thickness and composition uniformity for both GaAs/AlGaAs and InGaAs/InP layerstructures. In this paper we have used periodic multilayer structures and single layers to investigate thickness respectively composition uniformity. Thickness variations smaller than 1.5% (standard deviation) over a whole 2 inch wafer can be achieved. The standard deviation of a 2 inch wafer covered with InGaAs is as good as 1.4×10 -4 for the mismatch and 2.9 nm for the PL peak wavelength.

Atmospheric and low pressure shadow masked MOVPE growth of InGaAs(P)/InP and (In)GaAs/(Al)GaAs heterostructures and quantum wells

The shadow masked growth technique is presented as a tool to achieve thickness and bandgap variations laterally over the substrate during metalorganic vapor phase epitaxy. Lateral thickness and bandgap variations are very important for the fabrication of photonic integrated circuits, where several passive and active optical components need to be integrated on the same substrate. Several aspects of the shadow masked growth are characterized for InP based materials as well as for GaAs based materials. Thickness reductions are studied as a function of the mask dimensions, the reactor pressure, the orientation of the masked channels and the undercutting of the mask. The thickness reduction is strongly influenced by the mask dimensions and the reactor pressure, while the influence of the orientation of the channels and the amount of undercutting is only significant for narrow mask windows. During shadow masked growth, there are not only thickness variations but also compositional variations. Therefore, we studied the changes in In/Ga and As/P ratios for InGaAs and InGaAsP layers. It appears that mainly the In/Ga-ratio is responsible for compositional changes and that the As/P-ratio remains unchanged during shadow masked growth.

Selective and Shadow Masked MOVPE Growth of InP/lnGaAs(P) Heterostructures and Quantum Wells

Abstract We have investigated two growth techniques for lateral bandgap engineering over a substrate. Both selective growth and shadow masked growth can control the bandgap of the material by a thickness variation in combination with quantum well structures. We will present the main characteristics of these techniques and a device application: a multi-wavelength LED array grown in a single run with shadow masked growth.

Multiwavelength InGaAs/InGaAsP strained-layer MQW-laser array using shadow-masked growth

A simple technique for fabricating multiwavelength laser arrays is presented. The lateral variations in bandgap (or emission wavelength) between the different lasers are obtained by the use of shadow-masked growth. The shadow masked growth results in variations in thickness (and to a lesser extent, in composition) over the substrate. In combination with a multiquantum well (MQW) active region, this gives the required bandgap variations. By varying the window width in the shadow mask between 10 mu m and >500 mu m it was possible to obtain a wavelength span of 130 nm centered around 1.55 mu m. The strained-layer-ridge MQW Fabry-Perot lasers showed a constant threshold current (around 70 mA for an 11- mu m*500- mu m stripe).<<ETX>>

INFLUENCE OF THE NUCLEATION AND ANNEALING CONDITIONS ON THE QUALITY OF INP LAYERS GROWN ON GAAS BY MOCVD

Abstract InP layers have been grown on GaAs substrates using the two-step method [1]. The quality of the top InP layers is strongly affected by the growth parameters of the low-temperature nucleation layer. The influence of the growth velocity, temperature, thickness, annealing is shown and by optimization the full width at half maximum of X-ray rocking curves can be reduced to 428 arc sec for a 1.1 μm layer. The influence of post-growth annealing and thermal cycling during growth is described and by applying both methods, the photoluminescence intensity of 3 μm is increased by a factor of 4.

Selective MOVPE growth of GaAs on Si and its applications to LEDs

The two main problems still encountered during the growth of GaAs on Si are the lattice mismatch and the difference in thermal expansion coefficient. In this paper we will concentrate on the use of selective MOVPE growth of GaAs on Si and its applications to LED fabrication. The two reported techniques - small area selective growth and spatial control of microcrack formation through selective growth - resulted in higher yield and higher output power of IR-DH LEDs. By the implementations of thermal cycling procedures and the growth of an InGaAs/GaAs strained layer superlattice in the LED buffer layer we succeeded in increasing the output power over a factor of 5. For 3 μm GaAs on Si layers, we obtained X-ray FWHM values of 125 arc sec and etch pit density values of (1.0 ± 0.5)×106 cm-2.

Recent developments in relaxed and strained lattice mismatched heterostructures

Abstract The fabrication of novel optoelectronic devices and integrated circuits requires more ways of combining different materials. In this paper we will briefly review recent developments in the realization of relaxed and strained lattice mismatched heterostructures, with emphasis on GaAs and InP based material systems.