Optical properties of Zn-diffused InP layers for the planar-type InGaAs/InP photodetectors

Zn diffusion into InP was carried out ex-situ using a new Zn diffusion technique with zinc phosphorus particles placed around InP materials as zinc source in a semi-closed chamber formed by a modified diffusion furnace. The optical characteristics of the Zn-diffused InP layer for the planar-type InGaAs/InP PIN photodetectors grown by molecular beam epitaxy (MBE) has been investigated by photoluminescence (PL) measurements. The temperature-dependent PL spectrum of Zn-diffused InP samples at different diffusion temperatures showed that band-to-acceptor transition dominates the PL emission, which indicates that Zn was commendably diffused into InP layer as the acceptor. High quality Zn-diffused InP layer with typically smooth surface was obtained at 580 °C for 10 min. Furthermore, more interstitial Zn atoms were activated to act as acceptors after a rapid annealing process. Based on the above Zn-diffusion technique, a 50 μm planar-type InGaAs/InP PIN photodector device was fabricated and exhibited a low dark current of 7.73 pA under a reverse bias potential of −5 V and a high breakdown voltage of larger than 41 V (I < 10 μA). In addition, a high responsivity of 0.81 A/W at 1.31 μm and 0.97 A/W at 1.55 μm was obtained in the developed PIN photodetector.

Source:IOPscience

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Weakly doped InP layers prepared by liquid phase epitaxy using a modulated cooling rate

Epitaxial structures based on InP are widely used to manufacture a number of devices such as microwave transistors, light-emitting diodes, lasers and Gunn diodes. However, their temporary instability caused by heterogeneity of resistivity along the layer thickness and the influence of various external or internal factors prompts the need for the development of a new reliable technology for their preparation. Weak doping by Yb, Al and Sn together with modulation of the cooling rate applied to prepare InP epitaxial layers is suggested to be adopted within the liquid phase epitaxy (LPE) method. The experimental results confirm the optimized conditions created to get a uniform electron concentration in the active n-InP layer. A sharp profile of electron concentration in the n+-InP(substrate)/n-InP/n+-InP epitaxial structure was observed experimentally at the proposed modulated cooling rate of 0.3 °С–1.5 °С min−1. The proposed technological method can be used to control the electrical and physical properties of InP epitaxial layers to be used in Gunn diodes.

Source:IOPscience

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Growth of InP directly on Si by corrugated epitaxial lateral overgrowth

In an attempt to achieve an InP–Si heterointerface, a new and generic method, the corrugated epitaxial lateral overgrowth (CELOG) technique in a hydride vapor phase epitaxy reactor, was studied. An InP seed layer on Si (0 0 1) was patterned into closely spaced etched mesa stripes, revealing the Si surface in between them. The surface with the mesa stripes resembles a corrugated surface. The top and sidewalls of the mesa stripes were then covered by a SiO2 mask after which the line openings on top of the mesa stripes were patterned. Growth of InP was performed on this corrugated surface. It is shown that growth of InP emerges selectively from the openings and not on the exposed silicon surface, but gradually spreads laterally to create a direct interface with the silicon, hence the name CELOG. We study the growth behavior using growth parameters. The lateral growth is bounded by high index boundary planes of {3 3 1} and {2 1 1}. The atomic arrangement of these planes, crystallographic orientation dependent dopant incorporation and gas phase supersaturation are shown to affect the extent of lateral growth. A lateral to vertical growth rate ratio as large as 3.6 is achieved. X-ray diffraction studies confirm substantial crystalline quality improvement of the CELOG InP compared to the InP seed layer. Transmission electron microscopy studies reveal the formation of a direct InP–Si heterointerface by CELOG without threading dislocations. While CELOG is shown to avoid dislocations that could arise due to the large lattice mismatch (8%) between InP and Si, staking faults could be seen in the layer. These are probably created by the surface roughness of the Si surface or SiO2 mask which in turn would have been a consequence of the initial process treatments. The direct InP–Si heterointerface can find applications in high efficiency and cost-effective Si based III–V semiconductor multijunction solar cells and optoelectronics integration.

Source:IOPscience

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Fe Doping and Preparation of Semi-Insulating InP by Wafer Annealing under Fe Phosphide Vapor Pressure

Semi-insulating (SI) InP has been industrially produced by doping Fe atoms as deep acceptors. Fe concentrations in InP are, however, largely varied from top to tail along the crystal growth axis due to impurity segregation. In the present work, we have examined the possibility of vapor-phase Fe doping for fabrication of 50- and 75-mm-diameter SI InP wafers with constant Fe concentrations using a wafer annealing procedure. A small amount of Fe was charged with red phosphorus in ampoules in which InP wafers were annealed. It was found that the vapor-phase doping is effective for Fe doping of InP. The present technology can be applied for the fabrication of low Fe-doped SI InP wafers with similar Fe concentrations of all wafers from one InP ingot.

Source:IOPscience

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Modelling dislocation generation in high pressure Czochralski growth of InP single crystals: part II

The visco-plastic model developed in part I of this work is used here to study the dislocation evolution in high pressure Czochralski growth of InP single crystals. Towards this an in-house computational fluid dynamics code MASTRAPP is linked to the ABAQUS software. MASTRAPP has the capability to predict the thermal field history in the Czochralski furnace throughout the growth period. The thermal loading history determined through MASTRAPP is fed to ABAQUS and the visco-plastic constitutive equations are integrated while maintaining force equilibrium in the growing crystal. The combined model predicts the final dislocation densities in the crystal at the end of the growth period. It is then used to study and predict the effect of various parameters and phenomena on the final dislocation densities—thermal shock, gas convection, height of boric oxide encapsulant layer, marginal roles of thermal radiation and melt convection, and the cool down period. Gas convection is found to have the most significant effect on the dislocation densities.

Source:IOPscience

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