Abstract:Articles you may be interested inSub-250 nm room-temperature optical gain from AlGaN/AlN multiple quantum wells with strong band-structure potential fluctuations
“…Indeed, their high crystalline quality, resulting from the absence of extended defects such as dislocations or grain boundaries, should allow NW-based UV-light emitting devices (LEDs) to reach higher internal quantum efficiency (IQE) than their two-dimensional (2D) counterparts. High-efficiency UV-LEDs based on AlGaN and AlN NWs, with an IQE of 80% for AlN NW emitting at 210 nm, have been demonstrated recently, − whereas significantly lower IQEs have been reported so far in the 2D case, especially for short emission wavelengths. − It must be noted that efficiency improvement when using III-nitride alloy NWs is expected to be lower for the visible range, as conventional LEDs based on 2D heterostructures with In x Ga 1– x N (InGaN) already exhibit high IQEs attributed to very marked carrier localization in this alloy …”
We report on the structural and optical properties of AlxGa(1-x)N nanowire sections grown by plasma-assisted molecular beam epitaxy on GaN nanowire bases used as a template. Based on a combination of scanning electron microscopy, microphotoluminescence, time-resolved microphotoluminescence, and photon correlation experiments, it is shown that compositional fluctuations in AlxGa(1-x)N sections associated with carrier localization optically behave as quantum dots. Moreover, most of the micro-optical properties of such fluctuations are demonstrated to be very little dependent on kinetic growth parameters such as AlxGa(1-x)N growth temperature and AlN molar fraction in the alloy, which govern the macrostructural properties of AlxGa(1-x)N sections.
“…Indeed, their high crystalline quality, resulting from the absence of extended defects such as dislocations or grain boundaries, should allow NW-based UV-light emitting devices (LEDs) to reach higher internal quantum efficiency (IQE) than their two-dimensional (2D) counterparts. High-efficiency UV-LEDs based on AlGaN and AlN NWs, with an IQE of 80% for AlN NW emitting at 210 nm, have been demonstrated recently, − whereas significantly lower IQEs have been reported so far in the 2D case, especially for short emission wavelengths. − It must be noted that efficiency improvement when using III-nitride alloy NWs is expected to be lower for the visible range, as conventional LEDs based on 2D heterostructures with In x Ga 1– x N (InGaN) already exhibit high IQEs attributed to very marked carrier localization in this alloy …”
We report on the structural and optical properties of AlxGa(1-x)N nanowire sections grown by plasma-assisted molecular beam epitaxy on GaN nanowire bases used as a template. Based on a combination of scanning electron microscopy, microphotoluminescence, time-resolved microphotoluminescence, and photon correlation experiments, it is shown that compositional fluctuations in AlxGa(1-x)N sections associated with carrier localization optically behave as quantum dots. Moreover, most of the micro-optical properties of such fluctuations are demonstrated to be very little dependent on kinetic growth parameters such as AlxGa(1-x)N growth temperature and AlN molar fraction in the alloy, which govern the macrostructural properties of AlxGa(1-x)N sections.
“…We did not observe any Al clustering or compositional fluctuations as reported previously. 18 Details on AlN substrate preparation and MOCVD growth process can be found elsewhere. 19 Laser cavities were obtained by cleaving along the m-facet of the AlN wafer.…”
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“…In fact, room-temperature lasing at deep-UV wavelengths down to 214 nm has already been demonstrated with high-quality AlN layers using optical pumping [231]. Optical gain at wavelengths below 250 nm has also been measured with the variable-stripe-length method in AlGaN/AlN QWs featuring strong band-structure potential fluctuations [210,211,237], grown by plasma-assisted MBE under Ga-rich conditions as described previously in this article. Due to their advanced level of development and wide range of applications, a comprehensive description of III-nitride diode lasers is beyond the scope of this review.…”
This paper reviews the device physics and technology of optoelectronic devices based on semiconductors of the GaN family, operating in the spectral regions from deep UV to Terahertz. Such devices include LEDs, lasers, detectors, electroabsorption modulators and devices based on intersubband transitions in AlGaN quantum wells (QWs). After a brief history of the development of the field, we describe how the unique crystal structure, chemical bonding, and resulting spontaneous and piezoelectric polarizations in heterostructures affect the design, fabrication and performance of devices based on these materials. The heteroepitaxial growth and the formation and role of extended defects are addressed. The role of the chemical bonding in the formation of metallic contacts to this class of materials is also addressed. A detailed discussion is then presented on potential origins of the high performance of blue LEDs and poorer performance of green LEDs (green gap), as well as of the efficiency reduction of both blue and green LEDs at high injection current (efficiency droop). The relatively poor performance of deep-UV LEDs based on AlGaN alloys and methods to address the materials issues responsible are similarly addressed. Other devices whose state-of-the-art performance and materials-related issues are reviewed include violet-blue lasers, 'visible blind' and 'solar blind' detectors based on photoconductive and photovoltaic designs, and electroabsorption modulators based on bulk GaN or GaN/AlGaN QWs. Finally, we describe the basic physics of intersubband transitions in AlGaN QWs, and their applications to near-infrared and terahertz devices.
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