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Antimonide-Based Mid-Infrared Quantum-Well Diode Lasers
Published in M. O. Manasreh, Antimonide-Related Strained-Layer Heterostructures, 2019
Calculations were made structure A using the procedure of Ref. [52]. The conduction- and valence-band offsets for this structure were 195 and 65 meV, respectively. Fig. 38 shows the valence-subband structure. The compressive strain splits the heavy- and light-hole bands, resulting in the highest subband with a small in-plane effective mass (m = 0.063 m0) over a range of ∼ 15 meV. However, the top heavy-hole band is separated from the light-hole band by only ∼ 35 meV because of a relatively small strain (- 0.45%) and a large thickness (15 nm) of the well. The density of states for the conduction band is much smaller than that of the valence band. As the carrier density is increased, the electron quasi-Fermi level rises rapidly above the quantized level, while the hole quasi-Fermi level remains very close to the band edge.
Basics of Semiconductor Detector Devices
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
Also depicted in Fig. 15.9 are the quasi-Fermi levels Efn for electrons and Efp for holes.3 A quasi-Fermi level describes the population of electrons and holes separately in the conduction band and valence band when no longer in equilibrium, such as the case with applied voltage (forward or reverse) or other cases of charge injection, such as photoexcitation.
Transport Phenomena in Semiconductors
Published in Jyoti Prasad Banerjee, Suranjana Banerjee, Physics of Semiconductors and Nanostructures, 2019
Jyoti Prasad Banerjee, Suranjana Banerjee
The separate Fermi levels for the electrons and holes, i.e., quasi Fermi levels, provide a very powerful tool to solve non-equilibrium processes in semiconductors. Also, it is possible to study the properties of excess carriers using the same relationship between Fermi level and carrier density, as developed for the equilibrium process.
TCAD-Based Assessment of Dual-Gate MISHEMT with Sapphire, SiC, and Silicon Substrate
Published in IETE Technical Review, 2021
Preeti Singh, Vandana Kumari, Manoj Saxena, Mridula Gupta
As shown in Figure 4, high on state current (ION = 642 mA/mm) was achieved from the sapphire-based DG-MISHEMT as compared to the corresponding SiC- and Si-based devices, i.e. 454 and 377 mA/mm, respectively. This is due to the shift of bottom of conduction band energy level (EC) in the upward direction (with reference to electron quasi-fermi-level) in the case of SiC and Si substrate as compared to the reference structure, as shown in Figure 5. Due to the lower band gap of the silicon substrate, the improved potential at AlGaN/GaN heterointerface was seen in Figure 5 (than SiC and sapphire substrate materials) which results in lower 2DEG density. Therefore, 2DEG density at the AlGaN/GaN heterointerface reduces and leads to a positive threshold voltage along with lower drain current as visible from Figure 4. Figure 4 shows the comparison of drain conductance variation with a drain voltage for all the three cases. It is evident from the figure that silicon DG-MISHEMT with Si substrate results in reduced gd, i.e. lower drain voltage interference.
Augmenting the internal quantum efficiency of GaN-based green light-emitting diodes by sandwiching active region with p-AlGaN layers
Published in Journal of Modern Optics, 2020
Muhammad Usman, Abdur-Rehman Anwar, Munaza Munsif, Shahzeb Malik, Noor Ul Islam, Tariq Jamil
Figure 2(a–c) represent the calculated energy band profile of LED-I, -II and -III, respectively. LED-I is the conventional structure shown in Figure 2(a). In LED-II, the 1st GaN-barrier is replaced by Al0.05Ga0.95N as shown in Figure 2(b). The main objective of replacing the layer is to minimize the unbalanced carrier distribution (electrons/holes) across the active region due to the asymmetric properties of carriers. This behaviour leads to the degradation of optoelectronic properties [33]. The insertion of p- Al0.05Ga0.95N layer as a QB, enhances the band offset at the interface on the n-side. Additionally, by introducing p-AlGaN QB, the band diagram is raised on the n-side reducing the electron injection into the active region. This reduction is helpful to reduce the asymmetry between the concentration of electrons and holes in the active region. On the other hand, p-AlGaN QB injects holes in the active region as well which raises the hole concentration in comparison to LED-I. It may be noted that the valence quasi-fermi level is closest to the wells in LED-II than LED-I indicating better hole confinement (shown by dotted circles on the valence bands). In LED-III, the AlGaN EBL is graded with the increasing composition of Al from 0 to 15%, shown in Figure 2(c). The valence quasi-fermi level overlaps the quantum wells, the most, in LED-III than LED-II and LED-I. Thus, by combining the advantage of LED-II and graded EBL, a reasonably efficient device is achieved.
Time-resolved photoluminescence on double graded Cu(In,Ga)Se2 – Impact of front surface recombination and its temperature dependence
Published in Science and Technology of Advanced Materials, 2019
Thomas Paul Weiss, Romain Carron, Max H. Wolter, Johannes Löckinger, Enrico Avancini, Susanne Siebentritt, Stephan Buecheler, Ayodhya N. Tiwari
It is worth noting any error of and on . The lifetime directly influences the number of excess charge carriers (see Eqn. (12)), which affects the electron quasi-Fermi level logarithmically via Eqn. (13). Thus, an error of by a factor of 2 will change by (at room temperature). Similarly, a change of the doping by a factor of 2 will change the hole quasi-Fermi level by via Eqn. (14) and low excitation conditions (which is generally met under 1 sun illumination). Consequently, the difference of and can be explained by small deviations of the input parameters and . In particular, major deviations of are not expected as for instance reported for CIGS absorbers, which are influenced by trapping [6,35], where the measured decay time is in the order of 100 ns, while the simulation of the decay curve yielded only 1–20 ns.