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

Abstract

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 (−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.

Calibration of Polarization Fields and Electro-Optical Response of Group-III Nitride Based c-Plane Quantum-Well Heterostructures by Application of Electro-Modulation Techniques

“…The quantum well layer of nominal thickness 9.5 nm InGaN in InGaN/GaN and 4 nm InAlN in InAlN/GaN is sandwiched between two intrinsic GaN layers (i-GaN); the total thickness of the intrinsic (unintentionally doped) region is 23 nm in both the DHS and the GaN reference. The composition of the InGaN and InAlN layers was obtained from high-resolution x-ray diffraction scans (HRXRD) of the (0002) reflection [44][45][46]. The adjacent n-and p-GaN layer sequences contain, at the n-side, on top of the (0001) sapphire substrate: n-doped GaN:Si layer (200 nm, 3 × 10 18 cm −3 ), graded n-doped GaN:Si layer (100 nm, 10 18 -10 17 cm −3 ), low n-doped GaN:Si layer (400 nm, 1 × 10 17 cm −3 ); at the p-side: p-doped GaN:Mg (150 nm, 3 × 10 18 cm −3 ) capped with highly p-doped GaN:Mg contact layer (10 nm, 1 × 10 20 cm −3 ).…”

“…The electric performance of the group-III nitride semiconductor PIN-diodes analyzed in the present work by electroreflectance (ER) and electroluminescence (EL) spectroscopy in view of performance relevant electro-optical field effects was initially approached by capacitance-voltage measurements (CVM) in [44]. A brief review of the CVM measurement principles applied in [44][45][46] on the PIN-diodes studied by ER and EL is given in the following, since it has delivered the built-in potential V bi used to evaluate the polarization fields by ER.…”

“…Various methods utilizing the equivalent circuit characteristics can be addressed for accurate determination of the capacitance and the herewith related material and device properties, as reported in previous and recent publications [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60]. By application of CVM techniques, the capacitance C can be determined from the current in dependence of voltage I(V) characteristics using an equivalent circuit model to evaluate the resistances [46] or alternately fitted to the impedance complex function of a PIN-diode equivalent circuit [44]:…”

“…Accordingly, in the present work, the electro-optical response of model PIN-diodes based on group-III nitride double heterostructure (DHS) quantum wells (QWs) is studied by electroreflectance (ER) and electroluminescence (EL) spectroscopy and associated, for calibration purposes, with the internal electric fields. In addition, the strength and orientation of fields extracted by ER and EL modulation techniques are compared to field properties determined by capacitance-voltage measurements (CVM) on the model diodes in [44][45][46]. The materials used are exclusively wurtzite III-nitrides: AlN, InN, GaN, and ternary combinations of the binary compounds grown in the direction of the c-plane normal.…”

“…Accurate determination of emission energies and efficiencies in dependence of bias-voltage and frequency are acquired for the correct interpretation of the electro-optical device properties, which is a prerequisite for the implementation of III nitride materials based devices with favorable design parameters and sufficient output. N), in a double heterostructure (DHS) grown on (0001) sapphire substrate by metalorganic vapor-phase epitaxy (MOVPE), were fabricated and structurally characterized as described elsewhere [44][45][46]; the thickness of the central ternary nitride layer was determined there by high-resolution transmission electron microscopy (HRTEM). A PIN-diode with a GaN layer instead of InGaN or InAlN served as a reference sample.…”