AIGA Research Articles

Connecting Dots

Connecting Dots

InGaAs Communication Photodiodes: From Low- to High-Power-Level Designs

While InGaAs absorption material has been used for various applications up to 1.6-μm wavelength, specific designs for low-level detection have become of main interest using high responsivity and low-dark-current detectors. By adding an avalanche multiplication layer to form an avalanche photodiode (APD) using the Separated Absorption and Multiplication (SAM) structure, one can take advantage of the very low-noise properties of the multiplication process in large-bandgap AI(Ga)(ln)As material to improve receiver sensitivity by > 10 dB. Under high-power-level injection, specific PIN structures have been developed to improve space charge effects and linear operation as needed for power applications such as high bit rates using coherent detection or analog photonic links. Specific designs to achieve simultaneously broad bandwidth, high responsivity, very high power saturation, and high linearity will be discussed.

AIGA National Design Conference

AIGA National Design Conference

Analysis of MBE grown AI(x)Ga(1-x)As-GaAs heteroepitaxial layers by rutherford backscattering

The Rutherford Backscattering (RBS) technique has been optimized for the measurement of thin (>85A) alternating layers of A1(x)Ga(l-x)As and GaAs, which are at the limit of resolution of standard RBS measurements. RBS analysis of these structures provides both layer thicknesses and Al content. This information is useful for device processing since the layer thicknesses impact the FET threshold voltage and the Al content is important for proper selective chemical etching. Experimental conditions for the beam energy, detection angle, and sample rotation have been determined which allow measurement of the layer thicknesses to a precision of ±20-30A (for layers >85A) and of the Al content,x, to a precision of ±.02. Comparison of the RBS data with Transmission Electron Microscopy (TEM), Cathodoluminescence (CL), and Reflection High Energy Electron Diffraction (RHEED) measurements on the same material showed very good agreement between the different techniques. The advantage of RBS is that it can measure much thinner layers than CL and it provides thickness and composition information at the same time whereas TEM only provides thickness for this particular material. RBS is currently used tocharacterize a monitor wafer from each day’s run to provide a processing baseline for the MBE growth.

Synthesis, ion-exchange properties and analytical applications of iron(III) antimonate

Iron(III) antimonate is readily synthesized and shows excellent thermal and chemical stability. Distribution coefficients for 27 ions are presented. The separation possible include Mg—Sr, AI—Ga, Y—La, Mg—Cd—Zn, and Th—Sm.