Doping profile

Fig. 5. Bipolar transistor (a) schematic and (b) doping profiles of A, arsenic ion implanted into the silicon of the emitter ( -type) B, boron ion implanted into the silicon of the base (p-type) C, antimony ion implanted into the buried layer ( -type) and D, the epi layer...

To achieve the lowest possible delay a bipolar switching transistor developed by IBM minimizes parasitic resistances and capacitances. It consists of self-aligned emitter and base contacts, a thin intrinsic base with an optimized collector doping profile, and deep-trench isolation (36). Devices must be isolated from each other to prevent unwanted interactions in integrated circuits. While p—n junctions can be used for isolation, IBM s approach etches deep trenches in the siUcon wafer which are filled with Si02 to provide electrical insulation. 

Shallow doping profiles, particularly those of As, require nanoscale information on dopant distribution. Although SIMS can be reliably applied for layers below 5 nm... 

Fig. 7. Doping profiles for (a) p-type Si samples heat sunk during exposure to a 500 eV, 0.35mA cm-2 H+ beam for various periods and (b) similar samples not heat-sunk during ion bombardment (Horn et al., 1987).

A set of data obtained from an LEC [ITO/MEH-PPV PEO Li + OCA/A1] is shown in Figure 1.17. Since the junction is created in situ, the doping profile reverses when the bias... 

Figure 4.10 Damage and doping profiles for the same set of random as-implanted 6H-SIC samples, (a) Comparison between RBS-C measured and MC-BCA simulated damage profiles. (From [73]. 1999 Elsevier B.V. Reprinted with permission.) (b) Comparison between SIMS measured and MC-BCA simulated chemical profiles. (From [72]. 2001 Material Science Forum. Reprinted with permission.)...

Figure 4.12 Doping profiles of 60 keV Al ions implanted in 4H-SiC with different alignments of the beam direction with respect to the crystalline network. Parts (a) and (b) refer to wafers and part (c) refers to the-20 ones. The beam-to-crystal alignment per profile is given in the inset of each picture. Parts (a) and (c) are SIMS measurements and part (b) is an MC-BCA simulated profile. The concentration scale is normalized to the implantation dose. (From [23]. 2003 American Institute of Physics. Reprinted with permission.)...

The doping profiles in the entire device structure can be realized by epitaxial growth. 

Due to the extremely low diffusion coefficients in SiC, doping profiles in SiC DMOS transistors must be defined by successive implantation of aluminum (boron) for the base region and nitrogen (phosphorus) for the source. This resulted in a new name for a SiC DMOS transistor double-implanted MOSFET (DIMOSFET). 

Note that this is a very simplified case. A liquid junction, dual-layer insulator, trapped charges in the insulator, surface states at the insulator/semiconductor interface, channel doping profile, and multiple connecting metals have been omitted, for the sake of simplicity. They would be present in all real devices and situations, but would not affect the thought analysis in any significant way. 

If, on the other hand, the field forces the mobile holes away from the surface, a space charge region consisting of the ionized acceptor atoms, which are fixed in the lattice, forms over an appreciable distance into the semiconductor. The thickness of the surface space charge region is a function of the strength of the field at the surface and the semiconductor doping profile, as is the difference between the surface potential and the bulk potential of the semiconductor. If the surface potential deviates sufficiently far from the bulk potential, the surface will invert that is, it will contain an excess of mobile electrons. In this case, an -type conductive channel... 

Other arbitrary dope profiles can simply be realized by proper variation of the flow of germanium tetrachloride during deposition. 

For less highly-doped epi films, one can use the C-V method. In this case, use is made of the fact that a Schottky semiconductor diode has a voltage-dependent capacitance. In other words, when such a diode is reverse biased, a depletion layer forms which then has a capacitance determined by the depth of this layer (w) as well as the doping (N) at its edge. The doping profile can be determined from the following relations.9... 

For some doped layers, such as a low-dose ion implant for a MOS transistor, this procedure does not reveal the entire doping profile.10 In this case, a MOS structure is examined rather than a Schottky diode. Typically, a bare silicon wafer is oxidized, and then aluminum dots are sputtered on to form many MOS structures. When a MOS device is examined, Equations (8) and (9) have to be supplemented by... 

Figure 16 Doping profile for silicon wafer implanted with phosphorus, measured by C-V technique.10...

Gordon, B.J., On-line capacitance-voltage doping profile measurement... 

Consequently, this straightforward realization of vertical doping profiles and material mixtures enables precise layer fine-tuning to optimize device performance, for example power efficiency or lifetime [25]. For current OLED research and development and production [32, 33] doping and coevaporation are fundamental for device optimization and longer lifetimes. 

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