The fundamental problem in the investigation of the properties of a quantum dot is the calculation of the energy eigen
values of its confined charge carriers and evaluation of their corresponding wave functions. The quantum dots may be
approximated as spheres whose surfaces constitute infinite potential barriers for carriers. Consequently, the motion of
electrons and holes (which are confined inside the dot) can be analyzed by effective mass approximation applied to noninteracting
particles. An attempt has been made here to solve the Schrödinger’s equation for particles inside the infinite
spherical potential well to determine their allowed energy eigen values and eigen functions.
Optically sensitive binary, ternary and quaternary materials are now being explored for formation of heterojunctions which are capable to produce mm-waves MITATT mode. The source of saturation current injection can be excited by optical phonon radiation of suitable energy, which in turn can enhance the saturation current leading to the drop in carrier multiplication factor across the active zone of the p-n junction. The optical radiation at the edges of the depletion zone thus can affect the microwave performance of the homostructure/heterostructure DDRs. The authors have undertaken computer aided studies on optical control of mm- wave performance of several heterojunction DDRs, which can find application for optical detection/communication system. Heterojunctions of different base material like GaAs and InP are designed with the ternary material GaInAs to generate mm-waves with microwave frequencies centered around an window frequency of 94 GHz. The result have also ben compared with those of corresponding homostructure double drift diodes. The DDRs have been analyzed considering drift and tunnel current in MITATT mode. A double iterative computer method has been used to study the effect of optical injection on device properties of both homostructure and heterostructure DDR. The results indicate that the rf power output decreases with optical injection, which enables the DDR to be used as an optical detector.
IMPATT diodes can produce high power RF oscillation between a wide range of frequencies and excel some other solid state devices. The device technology for fabrication of silicon SDR diode is now very much advanced. The device efficiency and RF power output register sharp fall when the frequency of operation is enhanced to high values. Introduction of charge bump near the junction leading to formation of low- high-low profile by using ion implantation technique can be used to restore high efficiency and high power. The purpose of this paper is to study the ion implantation profiles of a low-high-low structure SDR and to suggest the optimized ion implantation parameters by using a computer simulation method developed by us. The method gives the best ion- implantation parameters of the charge bump suitable for use in fabrication of IMPATT diodes. The method is a generalized one and can be used to design high efficiency and high power silicon SDR for any frequency band. This can add to microelectronic manufacturing technologies.
Modulation of carrier multiplication factor in a reverse bias p—n junction can be realized through optical generation of carrier on either side of depletion layer which causes injection of photon—current along with thermal reverse saturation current into the denletion layer. The mm—wave characteristics of GaAs homo junction and GaAs/GaJnAs heterojunction in IMPATT and MITATT modes have been comDuted through device simulation process for wide range of values of carrier multiplication factor. The results indicate that the heterojunction provides considerably high efficiency compared to that of homo structure. The aprreciahle change i.n the ralue of diode negative resistance with photon injection (for low value of multiplication factor) would result in a fall in rf rower delivery from the diode. This property of changes in the out put power with change in multiplication factor can be used for detection of optical signal falling in the GaAs layer of both the homo and heterostructure diodes.
Keywords : IMPATT ,MITATT,Heterostructure,Homostructure,Negative resistance.
Microwave device characteristics of 35 GHz InP DDR have been obtained through accurate numerical simulation, and those are compared with the properties of Si and GaAs DDRs. The results indicate InP as a promising material for fabrication of IMPATT devices.