Net carrier concentration

The diffusion of hydrogen in highly or lightly silicon doped GaAs induces a modification of the electrical properties of the material a reduction of the free electron concentration (Fig. 2) and a significant increase of the electron mobility up to values close to the mobility in nonhydrogenated materials with the same net carrier concentration (Jalil et al., 1986 Pan... 

The net carrier concentration, shown in Fig. 7.8, was obtained at a frequency of 100 kHz. DLTS spectra were recorded using reverse- and forward-bias modes in the temperature range of 80-350 K. In the re verse-bias mode, the devices were reverse biased from -1.2V to -0.2V, with a pulse width of 1 ms. Two hole (majority-carrier) trap levels were found in all the devices. These levels were designated as Hi at I iv+0.26 and H2, for which an activation energy could not be resolved. Upon minority-carrier injection (forward-bias mode), DLTS showed two additional electron (minority-carrier) traps, which are labeled Ei (Ec-0.1eV) and E2 (Ec-0.83eV) in Table 7.1. The spectra were measured at an emission time of 465.2 s and the width of the... 

Figure 7.8. The net carrier concentration versus depth for the devices measured by C-V (DLTS measurements).The levels are designated for AP = autoplated (electroless deposition) EP = electroplated (electrodeposition) and PVD = physical vapor deposition. [Reproduced with permission from Ref. 95. Copyright 2001 Elsevier.]...

Figure 2. Donor ( ), acceptor (O), and net carrier ( ) concentrations as a function of baking time at 800 °C for growth of GaAs. (Reproduced with permission from reference 57. Copyright 1984 American Institute of...

The Hall effect provides a measure of the net carrier concentration of the dopants. Depending on the depth of the dopants, the activation of the impurity can be very much reduced. For example, Mg in GaN forms a level at 250 meV above the valence band, and the percentage of activation of the magnesium atoms at room temperature is about 1%. DLTS provides a measure of the deep states within the bandgap of the semiconductor. However, it only provides the activation energy and the impurity concentration, and it does not give the exact nature of the impurity concerned. Implantation experiments are required to correlate known impurities with the energy levels measured by DLTS. 

AlGaN alloys doped with Si have been grown by electron cyclotron resonance (ECR) MBE at temperatures between 700 and 800°C [23,24], These layers were found to have net carrier concentrations of 1016 to 1019 cm 3 as measured by the Hall effect technique. The carrier concentration varies only slightly on alloying up to 25% Al. The samples were found to be smooth and free from cracks. Murakami et al also reported crack-free surfaces of Si doped Alo.1Gao.9N with a carrier concentration of up to 2 x 1018 cm 3 [25],... 

The LTPL analysis revealed a 5 A shift in wavelength towards the blue part of the spectrum as compared with the one obtained for the non-stabilized porous Si substrate (LTPL spectra not shown). This again indicates a slight stress relief of 3C-SiC on the stabilized porous Si but, unfortunately, the film morphology was poor. However, it must be noted that a high net carrier concentration in all of the films studied, approximately mid 1018 cm-3, was estimated from the LTPL analysis. This inhibits the determination of the exact peak position due to the broadened peaks affected by the high doping level. 

Figure 2. Net carrier concentration and room temperature mobilities in Si-doped, n-type GaN as a function of SiH4 flow rate.

Hall measurements at temperatures where the shallow centres are fully ionized give the free-carrier concentration. This concentration can be assumed to be the net dopant concentration, but it does not determine the compensation or... 

Hall, and C-V, four-point probe and spreading resistance measurements to some extent provide a measure of the net impurity concentration of dopants in SiC ([ND - NA] or (Na - Nd]). In addition, Hall measurements provide a method for obtaining the mobility of the net carriers. These measurements have been applied to both n- and p-type SiC and its various polytypes. In this Datareview, we will report on the mobilities for most of the SiC polytypes under various growth conditions. 

To separate out the effect of the impurity changes at the junctions, we consider our basic equations (9.46) for the case where the temperature is constant but the carrier concentrations vary. These equations can then be integrated direetly, assuming no net current to flow, to give the eleetrochemical potential as... 

Laboratory-fortified blanks and matrix spikes both test the analyst s ability to obtain the expected result. The extent to which the net radionuclide concentration of the fortified blank (corrected for yield and radioactive decay) deviates from the expected value for the tracer radionuclide concentration is a measure of analytical bias. Any consistent deviation from the expected value should be investigated to eliminate the cause. Typical causes are the wrong counting efficiency, an analytical problem with interchange between carrier and tracer, unreliable yield determination, or erroneous tracer radionuclide concentration. 

The conductivity is proportional to the product of mobility and carrier concentration. If we have n charge carriers per unit volume, the net flux of charge carriers per unit time is given by n Vd and the current density J = I/A by... 

Fig. 2. Experimental set up for characterizing channel or carrier induced currents crossing the small area of a planar lipid bilayer which is schematically shown in enlarged view. Net current derives from either an applied potential or a concentration gradient...

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