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.
Using Fuzzy-Delphi technique to determine the concession period in BOT projects
BOT projects are affected by several risks and uncertainties. One of the most important issues in this type of contract is to determine the length of concession period considering these uncertainties. The previous studies have developed several models to determine the concession period. However, the uncertainties are not taking into account in most of the previous works. Moreover, none of the previous researches has the capability to aggregate the opinions of different experts being involved in a project regarding the values of the uncertain input parameters. In this research, a Fuzzy-Delphi technique is implemented to determine the length of concession period considering uncertainties. Using the proposed Fuzzy-Delphi technique, the values of different uncertain factors affecting a BOT project is determined considering opinions of a group of experts. The NPV value is calculated considering the resulted aggregated values of uncertain input parameters. Finally, the concession period is determined using fuzzy approach. A case study is conducted to evaluate the performance of the proposed methodology. It is shown that the concession period is determined more effectively using the proposed approach.