lunes, 28 de junio de 2010

PN - Junction

pn-Junction equilibrium

Peculiarity of Depletion Region in Diamond pn-Junction

Ionized dopant and carrier profiles in the pn-junction of diamond with a deep phosphorus donor and a boron acceptor are theoretically analyzed by simply solving a one-dimensional Poisson equation. The width of the depletion layer is around two times larger than that of the space-charge layer since there exists a transition region at the depletion layer edge. The difference between these widths is reduced with increasing temperature. It is predicted that the static saturation property of a bipolar pnp-junction transistor is affected by the large width of the depletion layer. A base donor density higher than high-1018 cm-3 is required for an acceptor density of 1×1018 cm-3 in the collector to obtain an Early voltage larger than 100 V. Similarly, a punch-through voltage is extremely reduced by the deep dopant effect. However, the deep dopant effect is weakened with increasing temperature.

Low-frequency noise and performance of GaN p-n junction photodetectors

We report on low-frequency noise characteristics of visible-blind GaN p-n junction photodetectors. Carrier hopping through defect states in the space charge region, believed to be associated with dislocations, is identified as the main mechanism responsible for the dark conductivity of the photodiodes. Under reverse bias, the dark current noise has the 1/f character and obeys the Hooge relation with α ≈ 3. Under forward bias, we observe generation-recombination noise related to a trap level with the activation energy of 0.49 eV. Under illumination, detectivity is found to be shot noise limited. The noise equivalent power of a 200×200 μm2 photodetector is estimated at6.6×10−15 W/Hz1/2 at a bias of −3 V. © 1998 American Institute of Physics.

Pn-junction delineation in Si devices using scanning capacitance spectroscopy

The scanning capacitance microscope (SCM) is a carrier-sensitive imaging tool based upon the well-known scanning-probe microscope (SPM). As reported in Edwards et al. [Appl. Phys. Lett. 72, 698 (1998)], scanning capacitance spectroscopy (SCS) is a new data-taking method employing an SCM. SCS produces a two-dimensional map of the electrical pn junctions in a Si device and also provides an estimate of the depletion width. In this article, we report a series of microelectronics applications of SCS in which we image submicron transistors, Si bipolar transistors, and shallow-trench isolation structures. We describe two failure-analysis applications involving submicron transistors and shallow-trench isolation. We show a process-development application in which SCS provides microscopic evidence of the physical origins of the narrow-emitter effect in Si bipolar transistors. We image the depletion width in a Si bipolar transistor to explain an electric field-induced hot-carrier reliability failure. We show two sample geometries that can be used to examine different device properties. © 2000 American Institute of Physics

Electrical simulation of scanning capacitance microscopy imaging of the pn junction with semiconductor probe tips

Scanning capacitance microscopy (SCM) enables the imaging of the two-dimensional carrier profiles of small transistors. Initial imaging utilized metal-coated probe tips but the limited resolution achievable with these tips due to their size led us to investigate micromachined silicon tips with a smaller tip diameter. Electrical simulations of a pnjunction structure probed with semiconducting tips indicate that image improvements result from the semiconductor nature of the silicon tips as well as from the smaller tip size. The tip becomes active in the imaging process as the capacitance–voltage responses of the tip and sample interact to improve image contrast and decrease theVbias dependence of the pn junction locations. SCM images of a 60 nm gate length n-metal–oxide–semiconductor device, obtained using a boron-doped silicon tip, demonstrate these effects. © 1999 American Institute of Physics.

Depletion region effects in Mg-doped GaN

The deep nature of the Mg acceptor will have important implications for the performance of high-speed GaN-based bipolar devices. In this work, the effect of the deep acceptor on the band bending within the depletion region is examined in detail. The width of the transition region, which separates the mobile holes from the space-charge edge, is carefully investigated. High-frequency modulation of the depletion region is discussed for both the large- and small-signal cases. For the small-signal case, calculated results are compared to experimental measurements of frequency-dependent capacitance which have been performed on Mg-doped GaN samples. . © 2000 American Institute of Physics.

Origin of conductivity and low-frequency noise in reverse-biased GaN p-n junction

We study the origins of conductivity and low-frequency noise in GaN p-n junctions under reverse bias. Carrier hopping through defect states in the space charge region is identified as the main mechanism responsible for low bias conductivity. Threading dislocations appear the most likely source of such defect states. At higher bias hopping is supplemented with Poole–Frenkel emission. A relatively high level of 1/f-like noise is observed in the diode current. The bias and temperature dependencies of the noise current are investigated.© 1998 American Institute of Physics.

Imaging of a silicon pn junction under applied bias with scanning capacitance microscopy and Kelvin probe force microscopy

Scanning capacitance microscopy (SCM) and Kelvin probe force microscopy (KPFM) are used to image the electrical structure of a silicon pn junction under applied bias. With SCM, the carrier density inside a diode is imaged directly. With KPFM, the surface potential distribution of an operating diode is measured, revealing different behavior from that in bulk. The surface potential drop is extended deep into the lightly p-doped region at reverse bias, reflecting the existence of the surface space-charge region as confirmed by the numerical simulation. © 2000 American Institute of Physics.

Theory of spin-polarized bipolar transport in magnetic p-n junctions

The interplay between spin and charge transport in electrically and magnetically inhomogeneous semiconductor systems is investigated theoretically. In particular, the theory of spin-polarized bipolar transport in magnetic p-n junctions is formulated, generalizing the classic Shockley model. The theory assumes that in the depletion layer the non equilibrium chemical potentials of spin-up and spin-down carriers are constant and carrier recombination and spin relaxation are inhibited. Under the general conditions of an applied bias and externally injected (source) spin, the model formulates analytically carrier and spin transport in magnetic p-n junctions at low bias. The evaluation of the carrier and spin densities at the depletion layer establishes the necessary boundary conditions for solving the diffusive transport equations in the bulk regions separately, thus greatly simplifying the problem. The carrier and spin density and current profiles in the bulk regions are calculated and the I-V characteristics of the junction are obtained. It is demonstrated that spin injection through the depletion layer of a magnetic p-n junction is not possible unless non equilibrium spin accumulates in the bulk regions—either by external spin injection or by the application of a large bias. Implications of the theory for majority spin injection across the depletion layer, minority spin pumping and spin amplification, giant magneto resistance, spin-voltaic effect, biasing electrode spin injection, and magnetic drift in the bulk regions are discussed in details, and illustrated using the example of a GaAs based magnetic p-n junction.© 2002 The American Physical Society

Infrared p-n-junction diodes in epitaxial narrow gap PbTe layers on Si substrates

The characteristics of p-n+ junctions in PbTe layers on Si(111) grown by molecular beam epitaxy are described. The temperature dependence of the leakage currents and ideality factors show that the junctions are generation-recombination limited over the 300–100 K range. The lifetimes deduced for the minority carriers (about 0.1 ns) suggest that their diffusion length is limited by the density of the threading dislocations, which was about 108 cm−2 for these heavily lattice mismatched layers. The theoretical diffusion limit at 200 K would be attained by reducing the dislocation density by a factor of 100. Such low densities have already been obtained in lead–chalcogenide layers on Si substrates by temperature cyclings. © 1999 American Institute of Physics.

Lenny Z Perez M

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