Graded bandgap ohmic contact to p-type zinc selenide and applications to transport studies, blue/green led and laser diodes
Abstract
In this thesis a low resistance ohmic contact to p-type ZnSe, ZnSSe and ZnMgSSe which involves the injection of holes from heavily doped ZnTe into ZnSe via a graded bandgap Zn(Se,Te) region is described. The specific contact resistance was characterized by a standard transmission line model measurement. To demonstrate the robustness of this new contact scheme at actual device current density, it was incorporated as an efficient injector of holes for laser diodes and LEDs. For a ZnCdSe/ZnSSe/ZnMgSSe separate confinement heterostructure, room temperature continuous wave lasing has been achieved at a threshold voltage of 5.5 volts. By the use of this contact, temperature-dependent Hall effect measurements were performed on a series of nitrogen doped ZnSe, ZnSSe and ZnMgSSe epilayers. The activation energy of nitrogen in ZnSe at the infinite dilution limit was extrapolated to be 114 meV. The result in this work is the first to show conclusively that nitrogen serves as a hydrogenic impurity in ZnSe. For ZnS$\rm\sb{0.8}Se\sb{0.92}$ and Zn$\rm\sb{0.93}Mg\sb{0.07}S\sb{0.14}Se\sb{0.86},$ the nitrogen accepter activation energies were found to be 97 meV, 177 meV respectively. The measurements were also performed on a lightly nitrogen doped ZnTe and we are the first to report the activation energy of nitrogen acceptor in ZnTe. A comparative study of nitrogen doping in ZnSe and ZnTe was performed and we found that, under normal growth conditions, it is the amount of nitrogen acceptors which can be incorporated in ZnSe, rather than the self-compensation process, that limits the p-type doping in ZnSe. The effects of Te isoelectronic impurity on the doping concentration in ZnSe:N were investigated. ZnSe-based multi-quantum well LEDs with Te isoelectronic doping in the active region was also studied. Strong green/yellow emission at room temperature has been observed at a forward bias of 2.5 volts.
Degree
Ph.D.
Advisors
Gunshor, Purdue University.
Subject Area
Electrical engineering|Electromagnetism|Condensation
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