We have evaluated the structural and optical properties of epitaxial layers grown on InP substrates patterned with Si02 masks. The effect of the mask on the MOVPE grown material surrounding and underlying the mask and the device performance from this material has been assessed in detail for the first time. This work is of considerable importance for the fabrication of optoelectronic integrated circuits (OEIC's), since the use of masks to fabricate different devices on the same wafer is a recognised method of achieving OEICs. The uniformity in composition of both GaInAs and GaInAsP (h=1.15pm) layers deposited on masked substrates has been evaluated using Auger, spatially resolved photoluminescence spectroscopy and imaging SIMS. A series of measurements were made on the epitaxial samples over distances ranging from within l p m of the mask to -250pm away. These measurements have shown that, in the case of this quaternary material, the composition is constant up to the edge of a 30 x 750pm widepask, ie no increase was seen in the In or P content on approaching the mask (within the resolution of the measurement techniques). For this quaternary material and mask geometry, no increase was seen in the growth rate thereby allowing planar epitaxial layers to be deposited, an important prerequisite for device integration. To further assess the quality of the selectively grown GaInAsP, ridge waveguides have been fabricated from material, both near to, and away from the masked features. Optical loss measurements (<3dB/cm) indicate no optical difference between these areas, confirming that the structural and optical quality of the selectively grown GaInAsP material is maintained. Laser structures integrated with a waveguide have been grown using optimised conditions, with the waveguide structure being grown selectively. In this type of structure two epitaxial growth stages are required (figure 1). In these multiple epitaxial growth stages it is essential that whilst good control of the selectively grown material is demonstrated, the 2nd growth stage does not adversely affect any exposed quaternary material deposited previously. TEM analysis has been performed on the areas around the mask (ie the junction between the laser and waveguide) to determine whether dislocations are present. This has shown that dislocations are present only at the vertical junction between the laser (1st growth) and waveguide (2nd growth) and that they are confined to within 1pm of the junction ie no dislocations were present at distances >-1pm from the mask edge. Such dislocations can be either a result of incorrect stabilisation of the epitaxial layers from the 1st growth stage or from growth next to a vertical roughened plane. SIMS and TEM studies have also been performed to determine if the Si02 mask induces any contaminatiodstrain etc in the structural or optical quality of the epitaxial material or substrate beneath the mask. Results will be presented which show that, depending on the geometry and size of the mask, the structural quality of the ...
advantages (increased values of To, reduced threshold current density, nse) have now been experimentally confirmed for long wavelength lasers uantum wells under biaxial compression. In addition, there are other ce (improved optical and carrier cocfinenmt, higher zanier iiijjection ance) when incorporating continuously graded confinement layers.sP/GaInAs MQW lasers by low pressure MOVPE will be described. wn with Ga,Inl_,As quantum wells either lattice matched (x=0.47) or P (h=1.25pm) barriers. The confinement region was either single pm), or was graded (GRIN-SCH) from GaInAsP (h=1.25pm) to ing the reagents to produce a continuous grade.een used for material characterisation. X-ray diffraction has .lO-4. Photoluminescence (PL) linewidths (FWHM) of 39meV ation in peak PL wavelength is less than +5 nm over a 2in. in abrupt hetero-interfaces in the quantum well region when ded confinement layers by Auger and secondary ion mass ed the continuous nature of the profile. a1 is compositionally homogeneous with precisely defined t layer profile. Results will be presented for these material ained on unstrained GaInAdGaInAsP (h=l. 15pm) MQW have been obtained.E Programme 1069 -Enhanced Performance Lasers for 69
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