Ultrathin InN Research Articles

Performance Improvement of InGaN-Based Red Light-Emitting Diodes via Ultrathin InN Insertion Layer

The serious separation of electron–hole wavefunctions, which is caused by the built-in electric field, prevents electron–hole radiative recombination in quantum wells (QWs) in high-In-content InGaN-based red light-emitting diodes (LEDs). Here, we propose a staggered structure that inserts an ultrathin InN layer in the single quantum well (SQW) to reduce the piezoelectric polarization and suppress the quantum confined Stark effect (QCSE). We have numerically simulated the effects of SQW with the InN insertion layer (IL) on the energy band structure and electron–hole wavefunctions of the red LED. Owing to alleviated piezoelectric polarization and improved overlaps of electron–hole wavefunctions, the simulation results have revealed that the internal quantum well (IQE) of the red LED with InN IL exhibits 42% higher than that of the red LED with a square-shaped QW (SSQW) at 60 A/cm2, and the efficiency droop ratio of red LED with InN IL is 48% lower than that of red LEDs with SSQW. Furthermore, we have found that the position of InN IL can affect the energy states of carriers, which has a great influence on the IQE and peak emission wavelength of red LEDs.

Electron mobility calculation for two-dimensional electron gas in InN/GaN digital alloy channel high electron mobility transistors

The InN/GaN digital alloy is a superlattice-like nanostructure formed by periodically stacking ultra-thin InN and GaN layers. In this study, we calculate the electron mobility in InN/GaN digital alloy channel high electron mobility transistors (HEMTs) by performing a single-particle Monte Carlo simulation. The results of the simulation show that alloy-induced scatterings have little impact and the electron mobility significantly improves as the effective indium mole fraction of the channel increases. This contrasts with InGaN alloy channel HEMTs, where alloy disorder and random dipole scatterings have a strong impact and the electron mobility decreases as the indium mole fraction of the channel increases.

Pentacene Coated Atop of Ultrathin InN Gas Sensor Device for the Selective Sensing of Ammonia Gas for Liver Malfunction Application

An ultrathin InN resistive gas sensor is used for selective sensing of ammonia gas by using (∼5nm) pentacene film coating on the InN epilayer for liver malfunction applications. In order to distinguish between ammonia and acetone gases in the exhaled breath, we used two physically different characteristics of InN epilayer such as bare InN epilayer and thin pentacene film atop InN epilayer. On the bare InN epilayer, current variation responses for 8ppm ammonia and 8ppm acetone were 0.6% and 0.57% respectively. On bare InN epilayer, the current variation response of ammonia gas is only 1.05 times the current variation response of acetone gas. On pentacene coated InN epilayer current variation responses for 8ppm ammonia and 8ppm acetone gases are 4.7% and 1.9% respectively. The current variation response for ammonia is 2.47 folds higher than acetone on the pentacene coated InN epilayer. A thin film pentacene atop InN epilayer is very effective to filter out the acetone gas. Therefore, pentacene coated atop ultrathin InN epilayer is useful for the selective sensing of the ammonia gas in the exhaled breath for liver malfunction applications.

Platinum Coating on an Ultrathin InN Epilayer as a Dual Gas Sensor for Selective Sensing of Ammonia and Acetone by Temperature Modulation for Liver Malfunction and Diabetes Applications

A platinum coating on an ultrathin InN resistive gas sensor was fabricated for the selective sensing of ammonia and acetone gas for liver malfunction and diabetes applications by using a temperature modulation technique. We use a cyclic temperature profile in the InN gas sensor heater, where the temperature varies from 200°C to 0°C and from 0°C to 200°C in increments of 50°C. Therefore, a different current variation response is measured on an InN epilayer for 5 ppm ammonia and 5 ppm acetone gas, respectively, because ammonia and acetone gas behave differently in the cyclic temperature profile. When ammonia and acetone gas are exposed in background air, the variation in the response of the current in different temperature regions is given as 2.5% for acetone gas and 7.85% for ammonia gas between 100°C to 150°C, and 12% for acetone gas and 8.85% for ammonia gas between 150°C to 200°C. Therefore, the temperature region 100°C to 150°C is suitable for selectively sensing ammonia gas for determining liver malfunction. The temperature range between 150°C to 200°C is suitable for selectively sensing acetone gas for the diabetes monitoring applications.

Optical properties of ultra-thin InN layer embedded in InGaN matrix for light emitters

We theoretically investigate the optical properties of an ultra-thin InN layer embedded in InGaN matrix for light emitters. The peak emission wavelength extends from ultraviolet (374 nm) to green (536 nm) with InN quantum well thickness increasing from 1 monolayer to 2 monolayers, while the overlap of electron-hole wave function remains at a high level (larger than 90%). Increase of In content in InGaN matrix provides a better approach to longer wavelength emission, which only reduces the spontaneous emission rate slightly compared with the case of increasing In content of the conventional InGaN quantum well. Also, the transparency carrier density derived from gain spectrum is of the same order as that in the conventional blue laser diode. Our study provides skillful design on the development of novel structure InN-based light emitting diodes as well as laser diodes.

Electron mobility of ultrathin InN on yttria-stabilized zirconia with two-dimensionally grown initial layers

An In-polar InN ultrathin film with high electron mobility was grown on an insulating yttria-stabilized zirconia (YSZ) (111) substrate via precise control of growth conditions for initial monolayers. It was found that the first several monolayers of InN on YSZ can be grown in a two-dimensional mode using extremely N-rich (ex-N-rich) conditions. Although the growth of more than several InN monolayers under these conditions results in rough surfaces, probably because of the suppressed migration of In atoms on the surface, the combination of ex-N-rich growth for the first few monolayers with subsequent conventional In-rich growth leads to the successful formation of InN films with smooth surfaces. The electron mobility of 11-nm-thick InN on YSZ with two-dimensionally grown initial layers was 170 cm2 V−1 s−1, which is much higher than the best reported value for InN ultrathin layers grown on GaN substrates. These results indicate that the structural quality of the InN/YSZ heterointerface and a smooth surface are inherently important for obtaining InN ultrathin films with good transport properties.

Polarization-Driven Topological Insulator Transition in aGaN/InN/GaNQuantum Well

Topological insulator (TI) states have been demonstrated in materials with a narrow gap and large spin-orbit interactions (SOI). Here we demonstrate that nanoscale engineering can also give rise to a TI state, even in conventional semiconductors with a sizable gap and small SOI. Based on advanced first-principles calculations combined with an effective low-energy k · p Hamiltonian, we show that the intrinsic polarization of materials can be utilized to simultaneously reduce the energy gap and enhance the SOI, driving the system to a TI state. The proposed system consists of ultrathin InN layers embedded into GaN, a layer structure that is experimentally achievable.

Investigation of optical properties of InGaN–InN–InGaN/GaN quantum-well in the green spectral regime

The optical properties of the InGaN/GaN quantum well with insertion of ultrathin InN layer is investigated by using the effective mass theory taking into account the valence band mixing effects. The total spontaneous emission radiation recombination rate can be optimized by modulating the position of InN layer in the InGaN QW. Meanwhile, it is observed that the difference of the spontaneous emission rate becomes smaller with increasing the sheet carrier density. Then, the influences of intermixing effect at the interface between InN and InGaN layers on the optical gain are analyzed. It shows the emission intensity is reduced as compared to the ideal QW structure while peak wavelength is red-shifted by ∼10 nm in the investigation range of L sn. Finally, the influence of partial strain relaxation on the lasing wavelength is discussed, which shows a blue shift of ∼27 nm in the case with residual strain of 50% in comparison to the no strain relaxation case.

Comparative cathodoluminescence characterization of ultrathin InN wells/GaN matrix MQWs grown on bulk‐GaN and MOVPE‐GaN

AbstractOne monolayer (1 ML) InN/GaN multiple quantum wells (MQWs) grown on bulk‐GaN and MOVPE‐GaN/ sapphire substrates with threading dislocation densities (TDDs) of about 106 cm–2 and 108 cm–2, respectively, were characterized by SEM‐CL measurements to study the effects of TDs on structural quality of InN/GaN MQWs. For the sample grown on bulk‐GaN substrate, step‐flow surface morphology and quite uniform spatial emission were observed as compared to the sample grown on MOVPE‐GaN/sapphire. CL peak energy at 86 K was observed at around 3.2 eV for both MQWs, but CL emission spectra from MQWs on bulk‐GaN substrate were five times stronger with smaller peak energy distribution, and full width at half maximum than those on MOVPE‐GaN substrate. This was caused by low‐TDD of bulk‐GaN substrate. Further, effects of growth temperature on 1 ML InN/GaN MQWs were investigated and it was found that CL peak energy tended to discretely shift to lower energy side, for e.g., from 3.18 eV to 2.9 eV when the growth temperature was decreased from 660 °C to 620 °C. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Detection of DNA Hybridization using Functionalized InN ISFETs

AbstractUltrathin (∼10 nm) InN ion sensitive field effect transistors (ISFETs) are functionalized by immobilized label-free oligonucleotide probes with 3-mercaptopropyltrimethoxysilane (MPTMS) through molecular vapor deposition (MVD) technique. This layer on the InN surface serves the function of selectively detecting the hybridization of complementary deoxyribonucleic acid (DNA). Using MVD technique to perform the gas-phase silanization of MPTMS provided a time-saving and simple method to reach 68° water contact angle after 1.5 h treatment. High resolution X-ray photoelectron spectroscopy (HRXPS) was employed to analyze the surface characteristics after functionalization. Modified probes DNA were covalently bonded to MPTMS-covered gate surface of InN ISFETs. And further hybridized with complementary DNA For a 12-mer oligonucleotide probe, a significant drain-source current decrease (∼ 6 μA) was observed for the hybridization with complementary DNA solution of 100 nM. In contrast, the noncomplementary DNA with single-base mismatch did not show obvious current changes. Functionalized ultrathin InN ISFETs for DNA sequence detection demonstrate the promise of biological sensing and genetic diagnosis applications.

Anion detection using ultrathin InN ion selective field effect transistors

Ultrathin (∼10nm) InN ion selective field effect transistors (ISFETs) have been demonstrated to perform ion sensing in aqueous solutions with a sensitivity of 5μA/decade and a response time smaller than 10s. The positively charged surface states on InN surfaces selectively adsorb anions, building Helmholtz voltages in solutions and modulating the drain-source current of the ISFETs. The ISFET performance is greatly enhanced by depleting carriers in the ultrathin InN channel where the film thickness is close to depth of surface electron accumulation.