No abstract

The conventional diamond cubic phase of silicon, so-called Si-I, exhibits the desirable semiconducting properties on which the silicon chip industry relies and it is by far the most stable of all silicon phases. However, other phases of silicon can be formed under pressure and some of them are metastable at room temperature and pressure. Two such phases, Si-III (BC8) and Si-XII (R8), can be produced by indentation with a diamond tip but, despite an understanding of their structure, little is known about their electrical properties. As we demonstrate experimentally, such phases can have entirely different (electrical) properties to normal (diamond cubic) silicon, consistent with recent theoretical studies that predict Si-XII to be a narrow-band-gap semiconductor and Si-III to be a semimetal. We report here electrical measurements on the Si-XII phase and demonstrate that it is indeed a semiconductor. Furthermore, and somewhat surprisingly, both boron and phosphorus can be electrically activated in the Si-XII structure during its formation by indentation at room temperature.

Conventional silicon devices are fabricated in the diamond cubic phase of silicon, so-called Si-I. Other phases of silicon such as Si-XII and Si-III can be formed under pressure applied by nanoindentation and these phases are metastable at room temperature and pressure. We demonstrate in this letter that such phases exhibit different electrical properties to normal ͑diamond cubic͒ silicon and exploit this to perform maskless, room temperature, electrical patterning of silicon by writing both conductive and insulating zones directly into silicon substrates by nanoindentation. Such processing opens up a number of potentially new applications without the need for high temperature processing steps.

Ground state lasing at 1.34 μ m from In As ∕ Ga As quantum dots grown by antimony-mediated metal organic chemical vapor deposition Appl. Phys. Lett. 90, 241110 (2007); 10.1063/1.2748082Ground-state lasing of stacked In As ∕ Ga As quantum dots with GaP strain-compensation layers grown by metal organic chemical vapor deposition Quantum dot lasers based on a stacked and strain-compensated active region grown by metal-organic chemical vapor depositionWe report on the lasing characteristics of three-and five-stack InAs/ GaAs quantum dot ͑QD͒ lasers grown by metal organic chemical vapor deposition. By increasing the number of stacked dot layers to 5, lasing was achieved from the ground state at 1135 nm for device lengths as short as 1.5 mm ͑no reflectivity coatings͒. The unamplified spontaneous emission and Z ratio as a function of injection current were also investigated. While the five-stack QD lasers behaved as expected with Z ratios of Ϸ2 prior to lasing, the three-stack QD lasers, which lased from the excited state, exhibited Z-ratio values as high as 4. A simple model was developed and indicated that high Z ratios can be generated by three nonradiative recombination pathways: ͑i͒ high monomolecular recombination within the wetting layer, ͑ii͒ Auger recombination involving carriers within the QDs ͑"unmixed" Auger͒, and ͑iii͒ Auger recombination involving both the QD and wetting layer states ͑"mixed" Auger͒, which dominate once the excited and wetting layer states become populated.

Analytical approach for strain and piezoelectric potential in conical self-assembled quantum dots J. Appl. Phys. 104, 083524 (2008); 10.1063/1.2999639 N incorporation into InGaAs cap layer in InAs self-assembled quantum dots Effects of seed layer on the realization of larger self-assembled coherent InAs/GaAs quantum dots Plan-view and cross-sectional transmission electron microscopy have been used for a detailed study of the defects formed in capped InAs/ GaAs quantum dot ͑QD͒ samples. Three main types of defects, V-shaped defects, single stacking faults, and stacking fault pyramids, were found to form under growth conditions that led to either very large, indium enriched, or coalesced islands. All three types of defects originate at the buried quantum dot layer and then travel through the GaAs cap to the surface on the ͕111͖ planes. The V-shaped defects were the most common and typically consisted of two pairs of closely spaced 60°Shockley partials with a ͗211͘ line direction. The two pairs originate together at the buried QD layer and then travel in "opposite" directions on different ͕111͖ planes. The second type of defect is the single stacking fault which consists of a single pair of partial dislocations separated by an Ϸ50 nm wide stacking fault. Finally, both complete and incomplete stacking fault pyramids were observed. In the case of the complete stacking fault pyramid the bounding dislocations along the ͓110͔, ͓110͔, ͓101͔, and ͓101͔ directions were identified as stair rods. A possible mechanism for the stacking fault pyramid formation, which can also account for the creation of incomplete stacking fault pyramids, is presented.