MOVPE grown Ga/sub 0.6/In/sub 0.4/Sb photodiodes for 2.55 mu m detection

Photodiodes with a long-wavelength cutoff extending out of 2.9 mu m have been fabricated from MOVPE-grown Ga/sub 0.6/In/sub 0.4/Sb homojunctions. These mesa devices without any passivation or antireflecting coating exhibit a peak efficiency as high as 43% at 2.60 mu m.<>     

Radiation damage and annealing behaviour in Be+-implanted pure Ga(Al)Sb layers

Implantation of Be⁺ ions into GaAISb epilayers is used to realize thep ⁺ layer of the Ga_0.96Al_0.04Sb p⁺/Ga_0.96Al_0.04Sbn ⁻ /GaSbn ⁺ (1.55 /Μm) avalanche photodetector whose performances are detailed in Ref. (1). The GaAISb layers are grown using liquid phase epitaxy (LPE); the quality of these as-grown layers is shown through photoluminescence and channeling measurements. The last part of this paper is devoted to the damaging level in the Be⁺-implanted layers. Some annealing techniques are presented as a mean of restoration of the implanted layers. It is clear from the results that the Be⁺ ion implantation leads to a low damage level in this III-V compound.     

GaInAsSb/GaSb pn photodiodes for detection to 2.4 mu m

Ga/sub 0.77/In/sub 0.23/As/sub 0.20/Sb/sub 0.80//GaSb pn heterojunction photodiodes have been prepared by liquid phase epitaxy. They exhibit a long-wavelength threshold of 2.4 mu m. The room-temperature dark current at V=-0.5 V is 3 mu A (10 mA/cm/sup 2/) and the external quantum efficiency is around 40% in the wavelength range 1.75-2.25 mu m. The estimated detectivity D* at 2.2 mu m is 8.8*10/sup 9/ cm Hz/sup 1/2/ W/sup -1/.<>     

Passivation of GaSb by sulfur treatment

Some features of the band structure of GaSb have led to a renewed interest in this material. It is well known that Ga(Al)Sb alloys are good candidates to realize avalanche photodetectors, due to their high hole kp/electron kn ionization coefficient ratio. In addition, recent studies have shown GaSb to be attractive for realizing tunneling barriers exhibiting a high value of the peak-to-valley current ratio or IR photodectectors. In order to optimize such devices, the passivation of GaSb is of great interest. Unfortunately, very few investigations have been reported in the literature on GaSb passivation. This paper reports experimental results concerning GaSb surface passivation using a chemical sulfuration method. Physicochemical analysis is attempted through ellipsometric, photoluminescence, and Auger electron spectroscopy measurements. Polluting oxygen and carbon agents are found to be removed from the surface using this process, leading to Schottky diodes of better quality. In addition, the sulfur treatment is shown to stabilize the cleaned surface.     

Growth and characterization of undoped and N-type (Te) doped MOVPE grown gallium antimonide

The growth of GaSb by MOVPE and itsn-type doping using a dimethyltellurium dopant source are investigated. The results of growth rate, morphology and Te incorporation as a function of growth parameters are given. Increasing growth temperature and V/III reactant ratio were found to reduce the Te incorporation. The lowest Hall carrier concentrations obtained at room-temperature, onp-type andn-type MOVPE GaSb are respectively:p _H= 2.2 × 10¹⁶cm⁻³ with a Hall mobility ofμ _H= 860 cm²/V.s andn _H= 8.5 × 10¹⁵cm⁻³ withμ _H= 3860 cm²/V.s. Furthermore, Hall mobilities as high as 5000 cm²/V.s were measured onn-type GaSb samples.     

Impact of the cutting dynamics of small radial immersion milling operations on machined surface roughness

This paper deals with a numerical and experimental study of the dynamics of flank milling operations at low cutting rates. It focuses on both properties of the cutting vibratory phenomena and their impacts on the roughness of the machined surface. The study is based on a one degree of freedom model of the mechanical machining system. The system is of the rigid cutter–flexible workpiece type. The cutting force model is based on the regenerative mechanism. The roughness of the surface machined at high speed revolutions has been studied for both forced vibrations occurring during stable cutting and self-excited vibrations occurring during unstable cutting. It is shown that forced vibrations have only a very slight impact (roughness remains quite similar to that obtained with a fully rigid mechanical system), while unstable cutting mainly impacts roughness. The stable milling zones can be shown on a roughness map. The study of the roughness shows that the boundary between stable and unstable cutting conditions, in the case of interrupted cutting, is a wide zone characterised by a doubling of the tooth passing period. In this zone, only one tooth over two is removing material due to the vibratory motion. A discussion explains the phenomenon.     

Resistivity and optical transmission of CuxS layers as a function of composition

Results are given concerning resistivities and optical transmission in the 0.45-2.5 μm range of Cu_xS layers as a function of composition x. The layers were fabricated by conventional vacuum evaporation; their compositions varied from x=1.89 to x=1.95 and their resistivities from 10^-2 to 10² ω cm. Optical transmission seems to be closely connected to resistivity.     

Fabrication du compose ternaire ZnGeP2 et caracterisation

Undoped or doped large single crystals of ZnGeP₂ have been elaborated. The growth technique is described. Crystallographic characteristics, electrical properties and optical transmission are studied. Our results are compared with the existing data of the literature.     

Fabrication and electrical properties of epitaxial layers of GaAs doped with manganese2

The method of fabrication of epitaxial layers of GaAs doped with Mn is described. Resistivity and Hall effect measurements are made on various samples in the temperature range 77–300°K. The experimental results are used to determine the densities N_a, N_d of acceptors and compensating donors, the activation energy E_a of the acceptor level associated with Mn and also the mobility of the carriers. These values are calculated using a model involving the two valence bands carriers. The results obtained confirm that the acceptor doping presents a saturation. They are compared to results previously published. A new value, rather close to unity, is obtained for the distribution coefficient of Mn in the case of low doping.     

A More Realistic Cutting Force Model at Uncut Chip Thickness Close to Zero

The relevance of the results of many machining simulations depends on the quality of the cutting force model used. Most of the cutting force models raise problems for uncut chip thickness close to zero. It is mainly due to the management of strong discontinuity and the infinitive limit of the cutting stiffness when the uncut chip thickness goes to zero. Furthermore, the correlation of these models with the experimental results is not very good at low and high uncut chip thickness. To resolve these difficulties, a new model of cutting force is proposed. It gets the advantage to be a continuous law with a finished limit of cutting stiffness when the uncut chip thickness goes to zero. The validation of this model with experimental results in milling and drilling shows a good correlation for a large variation of uncut chip thickness.