Optical properties of InGaN/GaN multi-quantum-well (MQWs) grown on sapphire and on Si(111) are reported. The tensile strain in the MQW on Si is shown to be beneficial for indium incorporation and Quantum-confined Stark Effect reduction in the multi-quantum wells. Raman spectroscopy reveals compressive strains of -0.107% in MQW on sapphire and tensile strain of +0.088% in MQW on Si. Temperature-dependent photoluminescence shows in MQW on sapphire a strong (30 meV peak-to-peak) S-shaped wavelength shift with decreasing temperature (6 K to 300K), whereas MQW on Si luminescence wavelength is stable and red-shifts monotonically. Micro-photoluminescence mapping over 200 by 200 μm2 shows the emission wavelength spatial uniformity of MQW on Si is 2.6 times higher than MQW on sapphire, possibly due to a more uniform indium incorporation in the multi-quantum-wells as a result of the tensile strain in MQW on Si. A positive correlation between emission energy and intensity is observed in MQW on sapphire but not in those on Si. Despite the lower crystal quality of MQW on Si revealed by atomic force microscopy, it exhibits a higher internal quantum efficiency (IQE) than MQW on sapphire from 6 K to 250 K, and equalizes at 300 K. Overall, MQW on Si exhibits a high IQE, higher wavelength spatial uniformity and temperature stability, while providing a much more scalable platform than MQW on sapphire for next generation integrated photonics.
more »
« less
Dependence of carrier escape lifetimes on quantum barrier thickness in InGaN/GaN multiple quantum well photodetectors
We reported significant improvements in device speed by reducing the quantum barrier (QB) thicknesses in the InGaN/GaN multiple quantum well (MQW) photodetectors (PDs). A 3-dB bandwidth of 700 MHz was achieved with a reverse bias of -6 V. Carrier escape lifetimes due to carrier trapping in the quantum wells (QWs) were obtained from both simulation and experimental fitting, identifying carrier trapping as the major speed limiting factor in the InGaN/GaN MQW PDs.
more » « less- Award ID(s):
- 1725797
- NSF-PAR ID:
- 10175856
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Express
- Volume:
- 28
- Issue:
- 16
- ISSN:
- 1094-4087; OPEXFF
- Page Range / eLocation ID:
- Article No. 23796
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
This paper presents alternate pairs of InGaN/GaN prestrained layers with varying indium compositions, which are inserted between the GaN/InGaN MQW active region and the n-GaN layer in a light-emitting diode (LED) nanostructure in order to obtain enhanced optical characteristics. The device is mounted on a silicon substrate followed by a GaN buffer layer that promotes charge injection by minimizing the energy barrier between the electrode and active layers. The designed device attains more than 2.897% enhancement in efficiency when compared with the conventional LED, which is attributed to the reduction of a polarization field within the MQW region. The proposed device with 15% indium composition in the prestrained layer attains a maximum efficiency of 85.21% and a minimized efficiency droop of 3.848% at an injection current of 40 mA, with high luminous power in the output spectral range. The device also shows a minimum blueshift in the spectral range, indicating a decrease in the piezoelectric polarization.
-
more » « less
Differential carrier lifetime measurements were performed on c-plane InGaN/GaN single quantum well (QW) light-emitting diodes (LEDs) of different QW indium compositions as well as with and without doped barriers. Mg-doped p-type and Si-doped n-type barriers close to the QW were used to reduce the net internal electric field in the QW, thereby improving the electron–hole wavefunction overlap on the LEDs. LEDs with doped barriers show short lifetimes and low carrier densities in the active region compared to the reference LEDs. The recombination coefficients in the ABC model were estimated based on the carrier lifetime and quantum efficiency measurements. The improvement in the radiative coefficients in the LEDs with doped barriers coupled with the blueshift of the emission wavelengths indeed indicates an enhancement in wavefunction overlap and a reduction of quantum confined Stark effect as a result of the reduced internal electric field. However, doped barriers also introduce non-radiative recombination centers and thereby increase the Shockley–Read–Hall (SRH) coefficient, although the increment is less for LEDs with high indium composition QWs. As a result, at high indium composition (22%), LEDs with doped barriers outperform the reference LEDs even though the trend is reversed for LEDs with lower indium composition (13.5%). Despite the trade-off of higher SRH coefficients, doped barriers are shown to be effective in reducing the internal electric field and increasing the recombination coefficients.
-
more » « less
Scanning tunneling electroluminescence (STL) microscopy is performed on a 3 nm‐thick InGaN/GaN quantum well (QW) with [In] = 0.23 such that the main light emission occurs in the green. The technique is used to map the radiative recombination properties at a scale of a few nanometers and correlate the local electroluminescence map with the surface topography simultaneously imaged by scanning tunneling microscopy. While the expected green emission is observed all over the sample, measurements performed on a 500 nm × 500 nm area around a 150 nm‐large and 2.5 nm‐deep hexagonal defect reveal intense emission peaks at higher energies close to the defect edges, features which are not visible in the macrophotoluminescence spectrum of the sample. Via a fitting of the local tunneling electroluminescence spectra, quantitative information on the fluctuations of the intensity, peak energy, width, and phonon replica intensity of the different spectral contributions is obtained, which provides information on carrier localization in the QW. This procedure also indicates that the carrier diffusion length on the probed area of the QW is shorter than 50 nm.
-
more » « less
Abstract High hole densities are desired in p‐channel field effect transistors to improve the speed and on‐currents. Building on the recently discovered undoped, polarization‐induced GaN/AlN 2D hole gas (2DHG), this work demonstrates the tuning of the piezoelectric polarization difference across the heterointerface by introducing indium in the GaN channel. Using careful design and epitaxial growths, these pseudomorphic (In)GaN/AlN heterostructures result in some of the highest carrier densities of >1014cm−2in a III‐nitride heterostructure—just an order below the intrinsic crystal limit of ≈1015cm−2. These ultra‐high density InGaN/AlN 2DHGs show room temperature mobilities of 0.5–4 cm2V−1s−1and do not freeze out at low temperatures. A characteristic alloy fluctuation energy of 1.0 eV for hole scattering in InGaN alloy is proposed based on the experiments.
