Self-assembled InGaN Quantum Dots Research Articles

Materials challenges for devices based on single, self-assembled InGaN quantum dots

Builiding on earlier studies of single InGaN quantum dots (QDs), we are considering their potential for use in blue- and green-emitting single photon sources. Envisaging a device based on a resonant cavity light emitting diode, we have studied the effect of growing QDs on an underlying AlN/GaN distributed Bragg reflector, and have shown that enhanced single QD emission may be obtained. Additionally, we have studied the effect of the growth and activation of a p-type cap on an underlying QD layer and have shown that the QDs survive the anneal process.

Ultraviolet light-emitting diodes with self-assembled InGaN quantum dots

A photoluminescence study showed that the self-assembled InGaN quantum dots (QDs) provide strongly localized recombination sites for carriers and that the piezoelectric field-induced quantum-confined Stark effect (QCSE) is small because the height of QDs is too small to separate the wave functions of electrons and holes. The InGaN QD light-emitting diode (LED) showed an emission peak at 400nm, and the peak was redshifted with increasing injection current, indicating a small QCSE. The light output power of an InGaN QD LED increased linearly with increasing injection current due to the strongly localized recombination sites of the InGaN QDs.

Characteristics of III-nitride photodiodes with self-assembled quantum dots

In this work, it has been demonstrated that metal–semiconductor–metal (MSM) photodiodes (PDs) with InGaN self-assembled quantum dots (QDs) were fabricated and compared with conventional InGaN MSM photodiodes. The scanning near-field optical microscope (SNOM) results revealed that such InGaN nanostructures could have better absorption for the near-field light with the wavelength of 457–514 nm. It was found that the InGaN QD photodiode with lower dark current can operate in the normal incidence mode; we could achieve a much larger photocurrent to dark current contrast ratio from MSM photodiodes with nanoscale InGaN quantum dots. It was also found that the measured responsivity of MSM photodiodes with QDs and without QDs approximated to the same in the range of 390–460 nm. Furthermore, the photodiodes with QDs showed higher spectral response than that of the photodiodes without QDs at wavelengths < 350 nm and > 480 nm.

InGaN self-assembled quantum dots grown by metal–organic chemical vapour depositionwith growth interruption

Self-assembled InGaN quantum dots (QDs) were grown by metal–organic chemical vapourdeposition with growth interruption at low V/III ratio and low growth temperature onsapphire substrates. The effects of the interruption time on the morphological and opticalproperties of InGaN QDs were studied. The results show that the growth interruption canmodify the dimension and distribution of InGaN QDs, and cause the QD emission wavelengthto blue shift with increasing interruption time. A density of InGaN QDs of about4.5 × 1010 cm−2 with an average lateral size of 11.5 nm and an average height of 1.6 nm can be obtained byusing a growth interruption time of 60 s.

Blue-green-red LEDs based on InGaN Quantum Dots by Plasma-assisted MBE using GaN QDs for Dislocation Filtering

ABSTRACTIn this paper, we report the development of blue-green-red LEDs based on InGaN quantum dots (QDs) and quantum wells in the active region, and GaN QDs in the nucleation layer for dislocation filtering, by plasma assisted molecular beam epitaxy. Self-assembled InGaN QDs and GaN QDs were grown in the Stranski-Krastanov mode. For the GaN QDs grown at 770 °C, the height distribution of the dots shows a bimodal distribution, which can be attributed to the interaction of the GaN QDs with the threading dislocations. TEM and XRD studies indicate that GaN QDs in the nucleation region help threading dislocations to deviate and annihilate. The average dot height, diameter and density of the InGaN QDs were estimated to be 3 nm, 30 nm and 7×1010 cm−2, respectively. The cathodoluminescence emission peak of the InGaN/GaN multiple layer quantum dots (MQDs) was found to red shift 330 meV with respect to the emission peak of the uncapped single layer of InGaN QDs due to Quantum Confined Stark effect. Blue LEDs based on InGaN/GaN multiple quantum wells (MQWs) as well as green and red LEDs based on InGaN MQDs emitting at 440 nm, 560 nm and 640 nm with FWHM of 30 nm, 87 nm and 97 nm, respectively, were grown and fabricated. The electroluminescence peak positions of both the green and red InGaN MQD LEDs are shown to be more blue-shifted with increasing injection current than that of the blue InGaN/GaN MQW LEDs.

Growth of InGaN self-assembled quantum dots and their application to photodiodes

Nanometer-scale InGaN self-assembled quantum dots (QDs) have been prepared by growth interruption during metalorganic chemical vapor deposition growth. With a 12 s growth interruption, we successfully formed InGaN QDs with a typical lateral size of 25 nm and an average height of 4.1 nm. The QD density was about 2×1010 cm−2. In contrast, much larger InGaN QDs were obtained without growth interruption. InGaN metal-semiconductor-metal photodiodes with and without QDs were also fabricated. It was found that the QD photodiode with lower dark current could operate in the normal incidence mode, and exhibit a stronger photoresponse.

InGaN quantum dot photodetectors

Nanometer-scale InGaN self-assembled quantum dots (QDs) have been prepared by growth stop during the metal-organic chemical vapor deposition growth. With a 12 s growth interruption, we successfully formed InGaN QDs with a typical lateral size of 25 nm and an average height of 4.1 nm. The QDs density was about 2 × 10 10 cm −2. Nitride-based QD metal–semiconductor–metal (MSM) photodetectors were also fabricated. It was found that we could significantly enhance the photocurrent to dark current contrast ratio of the MSM photodetectors by the use of QD structure.

A novel method to realize InGaN self-assembled quantum dots by metalorganic chemical vapor deposition

We report the use of an interrupted growth method in metalorganic chemical vapor deposition (MOCVD) to control the growth of InGaN layers and to grow nanoscale InGaN self-assembled quantum dots (QDs). With a 12-s growth interrupt, we successfully formed InGaN QDs with a typical lateral size of 25 nm and an average height of 4.1 nm. The QDs density is about 2×1010 cm −2. Strong photoluminescence (PL) emission of InGaN nanostructure was observed at a room temperature with a full-width-half-maximum (FWHM) of about 92 meV. These results suggest that such QDs are potentially useful in nitride-based optoelectronic devices.

Growth of nanoscale InGaN self-assembled quantum dots

It has been demonstrated that we can use interrupted growth mode in metalorganic chemical vapor deposition (MOCVD) to fabricate nanoscale InGaN self-assembed quantum dots (QDs). With a 12-s growth interruption, we successfully formed InGaN QDs with a typical lateral size of 25 nm and an average height of 4.1 nm. The QDs density is about 2×10 10 cm −2. In contrast, much larger InGaN QDs were obtained without growth interruption. Compared with samples prepared without growth interrupt, a much larger photoluminescence (PL) intensity and a large 67 meV PL blue shift was observed from samples prepared with growth interrupt. These results suggest such a growth interrupt method is potentially useful in nitride-based optoelectronic devices grown by MOCVD.

InGaN self-assembled quantum dots grown by metalorganic chemical-vapor deposition with indium as the antisurfactant

Nanometer-scale InGaN self-assembled quantum dots have been formed in an InGaN single-quantum-well structure on a (0001) sapphire substrate with In as the antisurfactant using low-pressure metalorganic chemical-vapor deposition. High-resolution transmission electron microscopy reveals that the average dimensions of InGaN nanometer-scale structures are as small as 4 nm wide and 1.5 nm high. Strong photoluminescence emission of the InGaN quantum dots was observed at room temperature with an emission peak of about 2.56 eV (485 nm) and a full width at half maximum of about 150 meV (30 nm). The choice of In as the antisurfactant also avoids the incorporation of foreign atoms in the active layers.

Growth of InGaN self-assembled quantum dots and their application to lasers

We have successfully grown InGaN self assembled quantum dots (QD's) on a GaN layer, using atmospheric-pressure metalorganic chemical vapor deposition (MOCVD). The average diameter of the QD's was as small as 8.4 nm, and strong emission from the QD's was observed at room temperature. Next, we have investigated a structure in which InGaN QD's were stacked to increase the total QD density. InGaN QD's were formed even when the number of stacked layers was ten. As the number of layers increased, the photoluminescence (PL) intensity increased drastically. Moreover, we have fabricated a laser structure with InGaN QD's embedded into the active layer. A clear threshold of 6.0 mJ/cm/sup 2/ was observed in the dependence of the emission intensity on the excitation energy at room temperature under optical excitation. Above the threshold, the emission was strongly polarized in the transverse electric (TE) mode, and the linewidth of the emission spectra was reduced to below 0.1 nm (resolution limit). The peak wavelength was around 405 nm. These results indicate lasing action at room temperature.

Narrow photoluminescence peaks from localized states in InGaN quantum dot structures

Microscopic photoluminescence spectra were measured for self-assembled InGaN quantum dots (QDs) grown by metalorganic chemical vapor deposition. A thin aluminum layer with 400 nm square apertures was formed on the sample surface to reduce the number of QDs measured. We observed very sharp peaks whose spectral linewidths were typically 170 μeV at 3.5 K, the linewidth being limited by spectral resolution. Such sharp lines were not observed in similar experiments on a reference sample having single InGaN quantum well structure. These experimental results suggest that excitons are strongly confined in our InGaN QD structure.

Self-assembled InGaN quantum dots grown by molecular-beam epitaxy

Self-assembled InGaN islands were grown by molecular-beam epitaxy on GaN, following a Stranski–Krastanow growth mode. Atomic force microscopy revealed that their dimensions were small enough to expect zero-dimensional quantum effects: the islands were typically 27 nm wide and 2.9 nm high. Strong blue-violet photoluminescence of the dots is observed, persisting up to room temperature. The temperature dependence of the photoluminescence is analyzed and compared to that of InGaN quantum well and bulk samples.

Nanometer-scale InGaN self-assembled quantum dots grown by metalorganic chemical vapor deposition

We have successfully grown nanometer-scale InGaN self-assembled quantum dots (QDs) on a GaN surface without any surfactants, using atmospheric-pressure metalorganic chemical vapor deposition. Atomic force microscopy shows that the average diameter of InGaN QDs is as small as 8.4 nm. Next, we have investigated the dependence of the QDs properties on the growth conditions: the amount of InGaN deposited and the growth temperature. Moreover, we have investigated the optical property of InGaN QDs, so that the strong emission was seen at 2.86 eV at room temperature.