Impact Of Doping Profile Research Articles

Impact of doping profiles on the formation of laser-active centers in bismuth-doped GeO2–SiO2 glass fibers

Multi-wavelength-band transmission technology based on the exploitation of the extended spectral region is considered as a potential approach to increase the transmission capacity in the deployed fiber-optic communication infrastructure. The development of optical amplifiers operating in the O-, E-, S-, and U-telecom bands is an extremely important challenge for the successful implementation of this technology. Bismuth-doped fibers are of increasing interest as gain materials, which can be used to provide broadband amplification in the mentioned telecom bands. This is due to the ability of Bi ions incorporated into glass network to form bismuth active centers (BACs) with specific optical properties, which are primarily determined by the glass modifiers. In this work, the impact of the doping profiles of both Ge atoms as glass modifiers and Bi ions on the BACs formation is studied using a series of bismuth-doped fibers fabricated by the modified chemical vapor deposition (MCVD) technique. The Bi-to-BACs conversion efficiency in various spatial regions of the studied samples is presented. It is turned out that for high-Bi concentration regions, the conversion efficiency is very low (less than 10%). In addition, the relationship of the conversion efficiency to the distribution of Bi ions and/or Ge atoms is discussed. Finally, a continuous-wave laser at 1.46 μm with a record slope efficiency of 80% is demonstrated using a Bi-doped fiber with confined doping profile, where the Bi-to-BACs conversion efficiency is 35%. This paper provides new information which might help to facilitate understanding of the features of Bi-doped fibers and their potentially achievable characteristics.

Design and application of ion-implanted polySi passivating contacts for interdigitated back contact c-Si solar cells

Ion-implanted passivating contacts based on poly-crystalline silicon (polySi) are enabled by tunneling oxide, optimized, and used to fabricate interdigitated back contact (IBC) solar cells. Both n-type (phosphorous doped) and p-type (boron doped) passivating contacts are fabricated by ion-implantation of intrinsic polySi layers deposited via low-pressure chemical vapor deposition and subsequently annealed. The impact of doping profile on the passivation quality of the polySi doped contacts is studied for both polarities. It was found that an excellent surface passivation could be obtained by confining as much as possible the implanted-and-activated dopants within the polySi layers. The doping profile in the polySi was controlled by modifying the polySi thickness, the energy and dose of ion-implantation, and the temperature and time of annealing. An implied open-circuit voltage of 721 mV for n-type and 692 mV for p-type passivating contacts was achieved. Besides the high passivating quality, the developed passivating contacts exhibit reasonable high conductivity (Rsh n-type = 95 Ω/□ and Rsh p-type = 120 Ω/□). An efficiency of 19.2% (Voc = 673 mV, Jsc = 38.0 mA/cm2, FF = 75.2%, and pseudo-FF = 83.2%) was achieved on a front-textured IBC solar cell with polySi passivating contacts as both back surface field and emitter. By improving the front-side passivation, a VOC of 696 mV was also measured.

Single-Event Response of the SiGe HBT Operating in Inverse-Mode

The single-event effect sensitivity of inverse-mode biased SiGe HBTs in both bulk and SOI technology platforms are investigated, for the first time, using digital circuits and stand-alone device test structures. Comparisons of heavy-ion broad beam data of shift register circuits constructed with forward-mode and inverse-mode biased SiGe HBTs from a first-generation, complementary SOI SiGe BiCMOS process, reveal an improvement in SEU mitigation for the inverse-mode shift register architecture. Full 3D TCAD simulations highlight the differences in transient current origination between forward and inverse-mode biased devices, illustrating the impact of doping profiles on ion-induced shunt duration. To extend the analysis to a bulk platform, new fourth-generation npn , SiGe HBTs were biased in both the forward and inverse-mode and irradiated at NRL using the two photon absorption measurement system. These measurements support the analysis of transient origination using 3D TCAD simulations. Furthermore, the isolation of the output terminal from the sensitive subcollector-substrate junction is experimentally demonstrated for the inverse-mode bias. Fully coupled mixed-mode simulations predict a significant reduction in sensitive area for inverse-mode shift registers built in a bulk SiGe platform.

Scanning voltage microscopy on active semiconductor lasers: the impact of doping profile near an epitaxial growth interface on series resistance

We apply scanning voltage microscopy to actively biased multiquantum-well ridge-waveguide semiconductor lasers. We localize the source of a major and hitherto unexplained sample-to-sample difference in current-voltage characteristics to the responsible junction. This is found to correspond to the regrowth interface, subsequently confirmed through secondary ion mass spectrometry to have different doping profiles in the two cases. By comparing the internal voltage profile of the operating lasers, we found that a voltage difference of 0.44 V occurred within /spl sim/100 nm of the regrowth interface in these laser structures, accounting for 88% of the difference in the measured series resistance. Additionally, 75% of the total device series resistance is associated with the structure's heterobarriers. These results relate nanoscopic measurements to macroscopic performance and are of significance in improving device understanding, design, and reliability.

Bandwidth improvement of a homojunction p-i-n photodiode

This paper presents an analytical study of the impact of doping profile in the p and n regions on the improvement of the bandwidth of a homo-junction p-i-n photodiode. In this study, nonuniformly doped p and n regions are considered. Thus, due to the nonuniformity in the doping, an electric field is established in both the p and n regions. Thereby, if the field is in the right direction, it will aid the diffusion of electrons and holes from p and n regions into the i region. Through these results, it is found that the bandwidth of the nonuniform photodiode is improved from 7 GHz, for uniformly doped p and n regions, to over 30 GHz. Whereas in this proposed structure, the bandwidth is comparable to that obtained for a double heterostructure photodiode, with the advantage of higher quantum efficiency.