Studies of InGaAs layers growth by metalorganic chemical vapor deposition for InP-HEMTs; Effects of trimethylindium and triethylindium
We studied an InGaAs epitaxial layers growth by metalorganic chemical vapor deposition (MOCVD) for InP-based high electron mobility transistors (HEMTs). The InGaAs channel layer of HEMTs was grown by a new material combination of triethylindium (TEI), triethylgallium (TEG) and arsine (AsH3). An electron mobility of the HEMTs structure sample was 20% higher than the one grown by trimethylindium (TMI), TEG and AsH3. And the DC characteristics of the HEMTs, the drain current and transconductance, were increased compared with the one. It is confirmed that this growth method is quite effective for the improvement of a characteristics of InP-based HEMTs
Photoluminescence spectra from δ-doped barrier layers in modulation-doped InAlAs/InGaAs field-effect transistor structures
The photoluminescence (PL) spectra from the Si δ-doped InAlAs barrier layers in modulation-doped InAlAs/InGaAs heterostructure field-effect transistor (HFET) structures with contact and recess-etch-stopper layers are investigated. A PL peak associated with the δ-doped layer (δ peak) is found. The δ-peak position shifts to shorter wavelength with increasing δ-doping concentration. The intensity reduction of the δ peak due to raising the temperature from 6 K is considerably slower than that of the exciton peak from the InAlAs buffer layer at about 8100 A, to which confined electrons and holes probably contribute. As a result, the δ-peak overwhelms the exciton peak and becomes the main peak of the InAlAs PL at temperatures higher than 40 K. The δ peak is not detected from HFET structures without the contact and recess-etch-stopper layers. The δ peak is attributed to the recombination of electrons from the δ-doped layer and photogenerated holes confined in the upper side of the barrier layer.
Shape and surface texture of molten droplets deposited on cold surfaces
When a molten droplet impacts on a cold surface, the interaction between solidification and fluid dynamics can lead to different shapes and surface textures of deposited droplets. This article presents an experimental study on deposition of small droplets (39 μm diameter) of molten wax ink on solid surfaces. Our results show that both the final shape and the surface texture of deposited droplets are extremely sensitive to deposition conditions, which include initial temperature of droplets, type of substrate surface and distance between substrate and printhead. Different surface textures are observed and shown to depend on the thermal and flow histories of ink droplets during the process of impact. A test using crystalline wax reveals crystallization as one of the major factors in determining the final texture.