Investigation of InAs/AlSb/GaSb-Based Structures and GaSb/AlSb/InAs/GaSb/AlSb/InAs Broken-Gap Interband Tunneling Structures
1997
Hochschulschrift
Zugriff:
85
In type I heterostructures like GaAs/AlGaAs, the bandgap of the wide-bandgap semiconductor covers all the bandgap of the narrow-bandgap one. Theconduction- band edge at one side is always higher in energy than the valence-band edge at the other side. By contrast, the band lineups betweenInAs and GaSb is peculia r, that is, the bottom of the InAs conduction bandis 0.15 eV lower in energy t han the top of the GaSb valence band. This type IImisaligned band lineup is di stinct from those in the type I heterostructures, the interband tunneling can be obtained readily. A new research field has been openedfor the InAs/AlSb/GaS b material system due to the unique band lineup. In theory, because the imper fect matching of the wave functions acrossthe type II interface, the conventio nal single-band effective mass equationwhich has been extensively applied to t he type I heterostructures can notbe utilized any longer. The model which will be used to investigate the type II heterostructures must take account of the coupling between conductionband and valence band. In this thesis, two three-b and models based on the k.pmethod are presented to investigate the InAs/AlSb/G aSb-based interband tunneling structures. The model which only considers the l ight particlecoupling is used to study the properties of the main negative dif ferentialresistance (NDR) observed in the room-temperature current-voltage cha racteristics. The coupling effects among conduction band, light-hole band,and split-off hole band are considered to construct the three-band CLS model.On th e other hand, due to the condensed carrier distribution at low temperature, th e weak heavy particle coupling has to be incorporated. The three-band CLH mode l including conduction band, light-hole band, andheavy-hole band is then used to investigate the low temperature characteristicsof interband tunneling struc tures. For the purpose of understanding the carrier transport in interband tu nnelingstructures, we first apply the CLS model to the investigation of two in terband tunneling structures ---GaSb/AlSb/InAs single-barrier andGaSb/AlSb/GaSb /AlSb/InAs double-barrier structures. The NDR mechanisms inthese structures ar e discussed. Based on the discussion, we then investigatethe other interband t unneling structures with the improved NDR characteristics.Two interband tunnel ing structures ---GaSb/InAs/GaSb/AlSb/InAs andGaSb/AlSb/InAs/AlSb/GaSb/AlSb/InA s triple-barrier structures arethen investigated.In GaSb/InAs/GaSb/AlSb/InAs s tructures, the effects of the InAs layersandwiched between GaSb layers are inv estigated. Without this InAs layer,just a GaSb/AlSb/InAs single-barrier struct ure results. The peak current densities and peak-to-valley current ratios of G aSb/InAs/GaSb/\-AlSb/InAsstructures are found higher than those of the single- barrier structure.With use of the CLS model, the higher peak current density i s found due tothe light-hole resonance in the GaSb well between the InAs layer and AlSbbarrier. With a 65\AA-thick GaSb well, the peak current density ofGaS b/InAs/GaSb/AlSb/InAs structure is always higher than that of thesingle-barrie r structure. Furthermore, the interaction between the conductionsubbands in th e InAs well and the light-hole subbands in the GaSb well isalso discussed. The subband-crossing has been observed after the subband-interaction-induced repu lsion.On the other hand, the origin of the NDR peak in the reverse I-Vcharacte ristics of GaSb/AlSb/InAs/AlSb/GaSb/AlSb/InAs triple-barrierstructures is disc ussed. The voltage across the AlSb center-barrier is found to block the tunnel ing through the conduction subbands in the InAs well.The reverse tunneling cur rent is then decreased, and a NDR would be foundunder reverse bias. In the se cond topic, the characteristics of the proposed GaSb/AlSb/InAs/GaSb/AlSb/InAs broken-gap interband tunneling (BGIT) structuresare demonstrated and investiga ted. An InAs layer is incorporated intothe well region of GaSb/AlSb/GaSb/AlSb/ InAs double-barrier interband tunneling(DBIT) structures to result in this str ucture. With the appropriate InAs wellthickness, the peak current density of t he BGIT structure is higher than that of the DBIT structure, and the peak-to-v alley current ratio is enhancedsignificantly. The variation of the room-temper ature I-V characteristics canbe interpreted reasonably using the CLS model. Mo reover, the peak current is found to vary exponentially with the AlSb-barrier layer thickness. TheInAs well and the AlSb layer thicknesses are both importan t structure parameters for optimizing the NDR characteristics of BGIT structur es.On the other hand, effects of the inelastic scattering on the interband tun neling, especially on the characteristics of BGIT structures, arediscussed. Be tter agreement with the experiments is found. In addition, the low-temperatur e I-V characteristics of BGIT structures aredemonstrated, which are found dist inct from the room-temperature ones.Some small peaks and kinks are observed at low temperature. With the three-band CLH model, the particular phenomena in t he low-temperature characteristics are found due to the heavy-hole coupling an d the in-planemomentum conservation. Finally, effects of the doping concentrat ion arediscussed and found to have pronounced influence on the low-temperature characteristics of BGIT structures.
Titel: |
Investigation of InAs/AlSb/GaSb-Based Structures and GaSb/AlSb/InAs/GaSb/AlSb/InAs Broken-Gap Interband Tunneling Structures
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Autor/in / Beteiligte Person: | Liu, Meng-Hwang ; 劉孟煌 |
Link: | |
Veröffentlichung: | 1997 |
Medientyp: | Hochschulschrift |
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