The transport properties of modulation, shifted modulation, and uniformly doped Al0.20Ga0.80N/GaN superlattices are presented. The modulation-doped sample is doped only in the AlGaN barriers. The shifted-modulation-doped sample has its dopants shifted by one-quarter period. Measurements reveal a strong improvement in mobility and resistivity for the modulation-doped and shifted-modulation-doped structures versus the uniformly doped structure. The modulation-doped sample has a mobility of 9.2 and 36 cm2/V s at 300 and 90 K respectively and a very low resistivity of 0.20 and 0.068 Ω cm at 300 and 90 K, respectively. Capacitance–voltage profiling shows multiple two-dimensional hole gases. The results are consistent with a reduction of neutral impurity scattering for modulation-doped structures as compared to uniformly doped structures.
Synchrotron radiation photoemission spectroscopy reveals enhanced oxygen incorporation in AlxGa1−xN as the Al mole fraction increases. It is shown that the increased oxygen donor incorporation can result in a conductivity-type change from p-type to n-type in Mg-doped AlxGa1−xN. Consistent with the conductivity-type change, epitaxial Al0.20Ga0.80N films exhibit n-type conductivity despite heavy Mg doping. The p-type conductivity of bulk AlxGa1−xN with a high Al mole fraction can be improved by employing AlxGa1−xN/AlyGa1−yN superlattices (SLs). At 300 K, Mg-doped Al0.17Ga0.83N/Al0.36Ga0.64N SLs (average Al mole fraction of 23%) exhibit strong p-type conductivity with a specific resistance of 4.6 Ω cm, a hole mobility of 18.8 cm2/Vs, and an acceptor activation energy of 195 meV.
Perpendicular transport characteristics of n-type AlxGa1−xN/GaN superlattices are presented. Planar and mesa-etched superlattice structures are employed to identify the perpendicular resistance. Perpendicular transport measurements in Al0.22Ga0.78N/GaN superlattices display linear current–voltage characteristics with a resistivity that is a factor of 6.6 higher than for bulk material. A theoretical model is developed for perpendicular transport in AlxGa1−xN/GaN superlattices based on sequential tunneling. The model shows that short superlattice periods are required to minimize the perpendicular resistivity.
Cross-plane electronic and thermal transport properties of p-type La0.67Sr0.33MnO3/LaMnO3 perovskite oxide metal/semiconductor superlattices J. Appl. Phys. 112, 063714 (2012) Polarization Coulomb field scattering in In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors J. Appl. Phys. 112, 054513 (2012) Modulation doping to control the high-density electron gas at a polar/non-polar oxide interface Appl. Phys. Lett. 101, 111604 (2012) Ultra low-resistance palladium silicide Ohmic contacts to lightly doped n-InGaAs
A technology for low-resistance ohmic contacts to III nitrides is presented. The contacts employ polarization-induced electric fields in strained cap layers grown on lattice-mismatched III-nitride buffer layers. With appropriate choice of the cap layer, the electric field in the cap layer reduces the thickness of the tunnel barrier at the metal contact/semiconductor interface. Design rules for polarization-enhanced contacts are presented giving guidance for composition and thickness of the cap layer for different III-nitride buffer layers. Experimental results for ohmic contacts with p-type InGaN and GaN cap layers are markedly different from samples without a polarized cap layer thus confirming the effectiveness of polarization-enhanced ohmic contacts.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.