Qinetiq Limited

The Secretary of State for Defence in Her Britannic Majesty's Government

Max-planck-gesellschaft Zur F&#xf6;rderung Der Wissenschaften E. V.

David John Robbins

Weng Y Leong

Gillian Fiona Marshall

Roger Timothy Carline

John L Glasper

Leigh Trevor Canham

John M Heaton

David R Wight

Keith G Barraclough

Christopher Pickering

David C W Herbert

Edward T R Chidley

Dieter H Bimberg

Steven W Birch

John Russell

Wang Y Leong

Allister W E Dann

Alan D Marrs

A photodetector circuit incorporates an APD detector structure () comprising a p&#x2212; silicon handle wafer () on which a SiOinsulation layer () is deposited in known manner. During manufacture a circular opening () is formed through the insulation layer () by conventional photolithography and etching, and an annular p+ substrate contact ring () is implanted in the handle wafer () after opening of the window (). The APD itself is formed by implantation of a p region () and an n+ region (). After the various implantation steps a metallisation layer is applied, and annular metal contacts are formed by the application of suitable photolithography and etching steps, these contacts comprising an annular contact () constituting the negative terminal and connected to the p+ substrate contact ring (), an annular metal contact () constituting the positive terminal and connected to the n+ region () of the APD, and source and drain contacts () and () (not shown in FIG.) connected to the source and drain of one or more CMOS MOSFET devices of the associated CMOS readout circuitry fabricated within a Si layer () formed on top of the insulation layer (). Such an arrangement overcomes the problem of combining APDs with CMOS circuits in that APDs operate at relatively high reverse bias (15-30V) and CMOS circuits operate at low voltage (SV), and the arrangement must be such as to prevent the high bias voltage from affecting the operation of adjacent CMOS transistors.

Photodiode detector and associated readout circuitry

A photodetector circuit incorporates an avalanche photodiode structure having a contact layer () forming an ohmic contact over an annular region () with the annular guard ring (). In the fabrication process, the starting substrate can either be the handle wafer of a p&#x2212; silicon-on-insulator wafer, or a p-Si substrate with an insulating SiOlayer (). A window () is produced in the insulating layer () by conventional photolithographic and etching. A n+ guard ring () is created by diffusing donor impurities into the substrate, and a thinner insulating SiOlayer () is thermally grown so as to cover the exposed surface of the substrate within the window (). P-type dopant is then implanted through the thin oxide layer to increase the doping level near the surface of the substrate. Subsequently a second window () is made in the insulating layer (), and the layer () is then epitaxially grown selectively on the area of the substrate exposed by the window () in the insulating layer (). The use of the thin oxide layer () reduces the area of the interface between the silicon of the layer () and the SiOof the layer () during the selective epitaxial deposition, thus leading to a reduction in the detrimental effect of the thermal expansion coefficient mismatch and producing less epitaxial defects at the window edge. After the epitaxial layer () has been grown the remaining part of the insulating layer () is removed by wet oxide etch which exposes an annular portion () of the underlying guard ring (). Subsequently a n+ silicon epi-poly layer () is deposited on the surface of the device, and forms an ohmic contact with the guard ring (), and simultaneously forms the top contact of the photodiode. Such a fabrication process does not significantly increase the fabrication complexity. Although an additional mask is required as compared with the conventional fabrication process, the fact that the layer () is in ohmic contact with the guard ring () means that it is no longer necessary to provide a separate contact to the guard ring, and as a result the overall number of masks or process steps used may be similar in both processes.

Avalanche photodiode with reduced sidewall defects

A horizontal access semiconductor photo detector () comprises a horizontal light absorbing layer () for converting light into photo-current which layer is configured to confine light within it in whispering gallery modes of propagation. The detector is configured to have a first waveguide portion () and a second light confining portion () arranged such that the waveguide portion couples light into the detector and transfers light into the light confining portion so as to excite whispering gallery modes of propagation around the light confining portion. The light absorbing layer may be part of the light confining portion or alternatively light can be coupled into the light confining portion or alternatively light can be coupled into the light absorbing layer from the light confining portion by evanescent coupling. The excitation of whispering gallery modes within the light absorbing layer significantly increases the effective absorption coefficient of the light absorbing layer.

Horizontal access semiconductor photo detector

A photodetector circuit incorporates an avalanche photodiode (APD) 300 produced by epitaxy on a CMOS substrate 302 with implanted n-well 304 and p-well 306. The n-well 304 has an implanted p+ guard ring 310 delimiting the APD 300. Within the guard ring 310 is an implanted n+ APD layer 312 upon which is deposited an epitaxial p+ APD layer 314, these layers forming the APD 300. The APD may be incorporated in an amplifier circuit 50 providing feedback to maintain constant bias voltage, and may include an SiGe absorption region to provide extended long wavelength response or lower avalanche voltage. Non-avalanche photodiodes may also be used.

Photodetector circuit

Layer processing to grow a layer structure upon a substrate surface comprises supplying a vapor mixture stream to the substrate ( ) to deposit constituents, monitoring growth with an ellipsometer ( ) and using its output in real-time growth control of successive pseudo-layers. A Bayesian algorithm is used to predict a probability density function for pseudo-layer growth parameters from initial surface composition, growth conditions and associated growth probabilities therewith, the function comprising discrete samples. Weights are assigned to the samples representing occurrence likelihoods based on most recent sensor output. A subset of the samples is chosen with selection likelihood weighted in favor of samples with greater weights. The subset provides a subsequent predicted probability density function and associated pseudo-layer growth parameters for growth control, and becomes a predicted probability density function for a further iteration of pseudo-layer growth.

Layer processing

Semiconductor substrate for reflecting electromagnetic radiation within

Silicon electroluminescent device

A method of monitoring surface layer growth using light scattered off a surface illuminated e.g. by a laser. A small area of a surface of a substrate is illuminated and the light scattered in a non-specular direction is detected during cleaning and subsequent layer growth. The amount of light scattered varies strongly with surface characteristics and gives clear indication of the end of oxide removal, initiation of nucleation and quality of growing layers. The monitoring is used during e.g. chemical vapor deposition, or e.g. molecular beam epitaxy growth processes.

Method and apparatus for monitoring surface layer growth

Pentaphosphates of the formula XP.sub.5 O.sub.14, wherein X is a rare earth metal, respond to incident ionizing radiation by emitting secondary electromagnetic radiation which may be visible or may be made visible by doping with other rare earth metal pentaphosphates or mixtures of Mn and Sb ions. The pentaphosphates of Ce and Pr respond quickly to cessation of incident radiation so that they are used to advantage in scintillators.

Luminescent material and preparation and use thereof

Growing community of inventors

Malvern, United Kingdom

David John Robbins