Precise determination of polarization fields in c-plane GaN/Al x Ga1-x N/GaN heterostructures with capacitance--voltage-measurements

Due to changes in the spontaneous and piezoelectric polarization, AlGaN/GaN heterostructures exhibit strong polarization fields at heterointerfaces. For quantum wells, the polarization fields lead to a strong band bending and a redshift of the emission wavelength, known as quantum-confined Stark effect. In this paper the polarization fields of thin AlGaN layers in a GaN matrix were determined by evaluating the changes in the depletion region width in comparison to a reference sample without heterostructure using capacitance-voltage-measurements. The polarization fields for Al0.09Ga0.91N (0.6 +/- 0.7 MV cm(-1)), Al0.26Ga0.74N (2.3 +/- 0.6 MV cm(-1)), Al0.34Ga0.66N (3.1 +/- 0.6 MV cm(-1)), Al0.41Ga0.59N (4.0 +/- 0.7 MV cm(-1)) and Al0.47Ga0.53N (5.0 +/- 0.8 MV cm(-1)) heterostructures were determined. The results of the field strength and field direction of all samples are in excellent agreement with values predicted by theory and a capacitance-voltage based Poisson-carrier transport simulation approach giving experimental evidence for a nonlinear increasing polarization field with Al-concentration. (C) 2019 The Japan Society of Applied Physic

Role of substrate quality on the performance of semipolar (11 2 - 2) InGaN light-emitting diodes

We compare the optical properties and device performance of unpackaged InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) emitting at ∼430 nm grown simultaneously on a high-cost small-size bulk semipolar (11 2 - 2) GaN substrate (Bulk-GaN) and a low-cost large-size (11 2 - 2) GaN template created on patterned (10 1 - 2) r-plane sapphire substrate (PSS-GaN). The Bulk-GaN substrate has the threading dislocation density (TDD) of ∼ and basal-plane stacking fault (BSF) density of 0 cm-1, while the PSS-GaN substrate has the TDD of ∼2 × 108cm-2 and BSF density of ∼1 × 103cm-1. Despite an enhanced light extraction efficiency, the LED grown on PSS-GaN has two-times lower internal quantum efficiency than the LED grown on Bulk-GaN as determined by photoluminescence measurements. The LED grown on PSS-GaN substrate also has about two-times lower output power compared to the LED grown on Bulk-GaN substrate. This lower output power was attributed to the higher TDD and BSF density

Accurate determination of polarization fields in (0 0 0 1) c-plane InAlN/GaN heterostructures with capacitance-voltage-measurements

In this paper the internal electric fields of nearly lattice matched InAlN/GaN heterostructures were determined. Pin-diodes containing InAlN/GaN heterostructures grown on (0 0 0 1) sapphire substrates by metalorganic vapour phase epitaxy were fabricated by standard lithography and metallization techniques. To determine the polarization fields in the InAlN quantum wells capacitance-voltage-measurements were performed on the pin-diodes. To reduce the measurement error, the heterostructure thicknesses were accurately determined by transmission electron microscopy. Large polarization fields, which correspond mainly to the spontaneous polarizations, for In0.15Al0.85N (5.9 +/- 0.8 MV cm(-1)), In0.18Al0.84N (5.4 +/- 0.9 MV cm(-1)) and In0.21Al0.79N (5.1 +/- 0.8 MV cm(-1)) quantum wells were observed. The results of the internal field strength and field direction are in excellent agreement with values predicted by theory and a CVM-based coupled Poisson/carrier transport simulation approach

Determination of polarization fields in group III-nitride heterostructures by capacitance-voltage-measurements

The polarization fields in wurtzite group III-nitrides strongly influence the optical properties of InAlGaN-based light emitters, e.g., the electron and hole wave function overlap in quantum wells. In this paper, we propose a new approach to determine these fields by capacitance-voltage measurements (CVM). Sheet charges generated by a change of the microscopic polarization at heterointerfaces influence the charge distribution in PIN junctions and therefore the depletion width and the capacitance. We show that it is possible to determine the strength and direction of the internal fields by comparing the depletion widths of two PIN junctions, one influenced by internal polarization fields and one without as a reference. For comparison, we conducted coupled Poisson/carrier transport simulations on the CVM of the polarization-influenced sample. We also demonstrate the feasibility and limits of the method by determining the fields in GaN/InGaN and GaN/AlGaN double heterostructures on (0001) c-plane grown by metal organic vapor phase epitaxy and compare both evaluation methods. The method yields (similar to 0.50 +/- 0.07) MV/cm for In0.08Ga0.92N/GaN, (0.90 +/- 0.13) MV/cm for Al0.18Ga0.82N/GaN, and (2.0 +/- 0.3) MV/cm for Al0.31Ga0.69N/GaN heterostructures. (C) 2016 AIP Publishing LLC