Flexbility of Ga-containing type-II superlattice for long-wavelength infrared detection

In this paper, the flexibility of long-wavelength Type-II InAs/GaSb superlattice (Ga-containing SL) is explored and investigated from the growth to the device performance. First, several samples with different SL period composition and thickness are grown by molecular beam epitaxy. Nearly strain-compensated SLs on GaSb exhibiting an energy band gap between 105 to 169 meV at 77K are obtained. Second, from electronic band structure calculation, material parameters are extracted and compared for the different grown SLs. Finally, two p-i-n device structures with different SL periods are grown and their electrical performance compared. Our investigation shows that an alternative SL design could potentially be used to improve the device performance of diffusion-limited devices for long-wavelength infrared detection

Optical properties of bimodally distributed InAs quantum dots grown on digital AlAs0.56Sb0.44 matrix for use in intermediate band solar cells

High-quality InAs quantum dots (QDs) with nominal thicknesses of 5.0–8.0 monolayers were grown on a digital AlAs0.56Sb0.44 matrix lattice-matched to the InP(001) substrate. All QDs showed bimodal size distribution, and their optical properties were investigated by photoluminescence (PL) and time-resolved PL measurements. Power dependent PL exhibited a linear relationship between the peak energy and the cube root of the excitation power for both the small QD family (SQDF) and the large QD family (LQDF), which is attributed to the type-II transition. The PL intensity, peak energy, and carrier lifetime of SQDF and LQDF showed very sensitive at high temperature. Above 125 K, the PL intensity ratio increased continuously between LQDF and SQDF, the peak energy shifted anomalously in SQDF, and the longer carrier radiative lifetime (≥3.0 ns at 77 K) reduced rapidly in SQDF and slowly in LQDF. These results are ascribed to thermally activated carrier escape from SQDF into the wetting layer, which then relaxed into LQDF with low-localized energy states

Electron and proton radiation effects on band structure and carrier dynamics in MBE and MOCVD grown III-V test structures

As part of a continuing study on radiation effects in photovoltaic materials, we exposed a series of AlGaAs/GaAs double heterostructures grown by molecular beam epitaxy and metalorganic chemical vapor deposition to electron and proton radiation. The active regions of the test articles were doped either unintentionally, p -type or n -type. Steady state and time resolved photoluminescence spectroscopy were used to characterize changes to the band structure and carrier dynamics. The effect of electron radiation on low temperature photoluminescence spectra and on room temperature carrier lifetime varied with dopant type and density. Steady-state photoluminescence reveals distinct effects from electron and proton exposures

महिषासुर: मिथक व परंपराएं

इक्कसवीं सदी के दूसरे दशक में भारत में महिषासुर आंदोलन द्विज संस्कृति के लिए चुनौती बनकर उभरा। इसके माध्यम से आदिवासियों, पिछड़ों और दलितों के एक बड़े हिस्से ने अपनी सांस्कृतिक दावेदारी पेश की। लेकिन यह आंदोलन क्या है, इसकी जड़ें समाज में कहां तक फैली हैं, बहुजनों की सांस्कृतिक परंपरा में इसका क्या स्थान है, मौजूदा लोक-जीवन में महिषासुर की उपस्थिति किन-किन रूपों में है, इसके पुरातात्विक साक्ष्य क्या हैं? गीतों-कविताओं व नाटकों में महिषासुर किस रूप में याद किए जा रहे हैं और अकादमिक-बौद्धिक वर्ग को इस आंदोलन ने किस रूप में प्रभावित किया है, उनकी प्रतिक्रियाएं क्या हैं? आदि प्रश्नों पर विमर्श हमें एक ऐसी बौद्धिक यात्रा की ओर ले जाने में सक्षम हैं, जिससे हममें अधिकांश अभी तक अपरिचित रहे हैं। क्या महिषासुर दक्षिण एशिया के अनार्यों के पूर्वज थे, जो बाद में एक मिथकीय चरित्र बन कर बहुजन संस्कृति के प्रतीक पुरुष बन गए? क्या यह बहुत बाद की परिघटना है, जब माकण्डेय पुराण, दुर्गासप्तशती जैसे ग्रंथ रच कर, एक कपोल-कल्पित देवी के हाथों महिषासुर की हत्या की कहानी गढ़ी गई? इस आंदोलन की सैद्धांतिकी क्या है? प्रमोद रंजन द्वारा संपादित किताब “महिषासुर: मिथक व परंपराएं” में लेखकों ने उपरोक्त प्रश्नों पर विचार किया है तथा विलुप्ति के कगार पर खड़े असुर समुदाय का विस्तृत नृवंशशास्त्रीय अध्ययन भी प्रस्तुत किया है। इस पुस्तक में समकालीन भारतीय साहित्य में महिषासुर पर लिखी गई कविताओं व गीतों का प्रतिनिधि संकलन भी है तथा महिषासुर की बहुजन कथा पर आधारित एक नाटक भी प्रकाशित है। समाज-विज्ञान व सांस्कृतिक विमर्श के अध्येताओं, सामाजिक-राजनीतिक कार्यकर्ताओं, साहित्य प्रेमियों के लिए यह एक आवश्यक पुस्तक है

Electrically pumped quantum-dot lasers grown on 300 mm patterned Si photonic wafers

Monolithic integration of quantum dot (QD) gain materials onto Si photonic platforms via direct epitaxial growth is a promising solution for on-chip light sources. Recent developments have demonstrated superior device reliability in blanket hetero-epitaxy of III-V devices on Si at elevated temperatures. Yet, thick, defect management epi designs prevent vertical light coupling from the gain region to the Si-on-Insulator waveguides. Here, we demonstrate the first electrically pumped QD lasers grown by molecular beam epitaxy on a 300 mm patterned (001) Si wafer with a butt-coupled configuration. Unique growth and fabrication challenges imposed by the template architecture have been resolved, contributing to continuous wave lasing to 60 °C and a maximum double-side output power of 126.6 mW at 20 °C with a double-side wall-plug efficiency of 8.6%. The potential for robust on-chip laser operation and efficient low-loss light coupling to Si photonic circuits makes this heteroepitaxial integration platform on Si promising for scalable and low-cost mass production