p–n junction

Abstract: In a single crystal of semiconductor the impurity concentration may vary from p-type to n-type producing a mechanically continuous rectifying junction. The theory of potential distribution and rectification for p-n junctions is developed with emphasis on germanium. The currents across the junction are carried by the diffusion of holes in n-type material and electrons in p-type material, resulting in an admittance for a simple case varying as (1 + iωτ p )1/2 where τ p is the lifetime of a hole in the n-region. Contact potentials across p-n junctions, carrying no current, may develop when hole or electron injection occurs. The principles and theory of a p-n-p transistor are described.

Abstract: Few-layer black phosphorus, a new elemental 2D material recently isolated by mechanical exfoliation, is a high-mobility layered semiconductor with a direct bandgap that is predicted to strongly depend on the number of layers, from 0.35 eV (bulk) to 2.0 eV (single-layer). Therefore, black phosphorus is an appealing candidate for tunable photodetection from the visible to the infrared part of the spectrum. We study the photoresponse of field-effect transistors (FETs) made of few-layer black phosphorus (3 nm to 8 nm thick), as a function of excitation wavelength, power and frequency. In the dark state, the black phosphorus FETs can be tuned both in hole and electron doping regimes allowing for ambipolar operation. We measure mobilities in the order of 100 cm2/V s and current ON/OFF ratio larger than 103. Upon illumination, the black phosphorus transistors show response to excitation wavelengths from the visible up to 940 nm and rise time of about 1 ms, demonstrating broadband and fast detection. The responsivity reaches 4.8 mA/W and it could be drastically enhanced by engineering a detector based on a PN junction. The ambipolar behavior coupled to the fast and broadband photodetection make few-layer black phosphorus a promising 2D material for photodetection across the visible and near-infrared part of the electromagnetic spectrum.

Abstract: I. SEMICONDUCTOR FUNDAMENTALS. 1. Semiconductors -- A General Introduction. General Material Properties. Crystal Structure. Crystal Growth. 2. Carrier Modeling. The Quantization Concept. Semiconductor Models. Carrier Properties. State and Carrier Distributions. Equilibrium Carrier Concentrations. 3. Carrier Action. Drift. Diffusion. Recombination -- Generation. Equations of State. Supplemental Concepts. 4. Basics of Device Fabrication. Fabrication Processes. Device Fabrication Examples. R1. Part I Supplement and Review. Alternative/Supplemental Reading List. Figure Sources/Cited References. Review List of Terms. Part I Review Problem Sets and Answers. IIA. PN JUNCTION DIODES. 5. PN Junction Electrostatics. Preliminaries. Quantitative Electrostatic Relationships. 6. PN Junction Diode -- I-V Characteristics. The Ideal Diode Equation. Deviations from the Ideal. Special Considerations. 7. PN Junction Diode -- Small-Signal Admittance. Introduction. Reverse-Bias Junction Capacitance. Forward-Bias Diffusion Admittance. 8. PN Junction Diode -- Transient Response. Turn-Off Transient. Turn-On Transient. 9. Optoelectronic Diodes. Introduction. Photodiodes. Solar Cells. LEDs. IIB. BJTS AND OTHER JUNCTION DEVICES. 10. BJT Fundamentals. Terminology. Fabrication. Electrostatics. Introductory Operational Considerations. Performance Parameters. 11. BJT Static Characteristics. Ideal Transistor Analysis. Deviations from the Ideal. Modern BJT Structures. 12. BJT Dynamic Response Modeling. Equivalent Circuits. Transient (Switching) Response. 13. PNPN Devices. Silicon Controlled Rectifier (SCR). SCR Operational Theory. Practical Turn-on/Turn-off Considerations. Other PNPN Devices. 14. MS Contacts and Schottky Diodes. Ideal MS Contacts. Schottky Diode. Practical Contact Considerations. R2. Part II Supplement and Review. Alternative/Supplemental Reading List. Figure Sources/Cited References. Review List of Terms. Part II Review Problem Sets and Answers. III. FIELD EFFECT DEVICES. 15. Field Effect Introduction -- the J-FET and MESFET. General Introduction. J-FET. MESFET. 16. MOS Fundamentals. Ideal Structure Definition. Electrostatics -- Mostly Qualitative. Electrostatics -- Quantitative Formulation. Capacitance-Voltage Characteristics. 17. MOSFETs -- The Essentials. Qualitative Theory of Operation. Quantitative ID - VD Relationships. ac Response. 18. Nonideal MOS. Metal-Semiconductor Workfunction Difference. Oxide Charges. MOSFET Threshold Considerations. 19. Modern FET Structures. Small Dimension Effects. Select Structure Survey. R3. Part III Supplement and Review. Alternative/Supplemental Reading List. Figure Sources/Cited References. Review List of Terms. Part III Review Problem Sets and Answers. Appendix A. Elements of Quantum Mechanics. Appendix B. MOS Semiconductor Electrostatics -- Exact Solution. Appendix C. MOS C-V Supplement. Appendix D. MOS I-Vsupplement. Appendix E. List of Symbols. Appendix M. MATLAB Program Script.

Abstract: The ability to detect light over a broad spectral range is central to practical optoelectronic applications and has been successfully demonstrated with photodetectors of two-dimensional layered crystals such as graphene and MoS2. However, polarization sensitivity within such a photodetector remains elusive. Here, we demonstrate a broadband photodetector using a layered black phosphorus transistor that is polarization-sensitive over a bandwidth from ∼400 nm to 3,750 nm. The polarization sensitivity is due to the strong intrinsic linear dichroism, which arises from the in-plane optical anisotropy of this material. In this transistor geometry, a perpendicular built-in electric field induced by gating can spatially separate the photogenerated electrons and holes in the channel, effectively reducing their recombination rate and thus enhancing the performance for linear dichroism photodetection. The use of anisotropic layered black phosphorus in polarization-sensitive photodetection might provide new functionalities in novel optical and optoelectronic device applications. The anisotropic optical properties of black phosphorus can be exploited to fabricate photodetectors with linear dichroism operating over a broad spectral range.