This paper presents growth orientation dependence of the piezoelectric polarization of InxGa1−xN and AlyGa1−yN layers lattice matched to GaN. This topic has become relevant with the advent of growing nitride based devices on semipolar planes [A. Chakraborty et al., Jpn. J. Appl. Phys., Part 2 44, L945 (2005)]. The calculations demonstrate that for strained InxGa1−xN and AlyGa1−yN layers lattice matched to GaN, the piezoelectric polarization becomes zero for nonpolar orientations and also at another point ≈45° tilted from the c plane. The zero crossover has only a very small dependence on the In or Al content of the ternary alloy layer. With the addition of spontaneous polarization, the angle at which the total polarization equals zero increases slightly for InxGa1−xN, but the exact value depends on the In content. For AlyGa1−yN mismatched layers the effect of spontaneous polarization becomes important by increasing the crossover point to ∼70° from c-axis oriented films. These calculations were performed u...

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Strain-induced polarization in wurtzite III-nitride semipolar layers

This paper reviews current technological developments in polarization engineering and the control of the quantum-confined Stark effect (QCSE) for InxGa1- xN-based quantum-well active regions, which are generally employed in visible LEDs for solid-state lighting applications. First, the origin of the QCSE in III-N wurtzite semiconductors is introduced, and polarization-induced internal fields are discussed in order to provide contextual background. Next, the optical and electrical properties of InxGa1- xN-based quantum wells that are affected by the QCSE are described. Finally, several methods for controlling the QCSE of InxGa1- xN-based quantum wells are discussed in the context of performance metrics of visible light emitters, considering both pros and cons. These strategies include doping control, strain/polarization field/electronic band structure control, growth direction control, and crystalline structure control.

Control of Quantum-Confined Stark Effect in InGaN-Based Quantum Wells

We fabricated a phosphor-conversion white light emitting diode (LED) using an InGaN chip that emits 400 nm near-ultraviolet (n-UV) light and phosphors that emit in the blue and yellow region. When the white LED was operated at a forward-bias current of 20 mA at room temperature (RT), the color temperature (Tcp), average color rendering (Ra), operating voltage (Vf) and luminous efficacy (ηL) were estimated to be 5800 K, 85.3, 3.2 V, and 26.1 lm/W, respectively. With increasing forward-bias current, the luminous flux increased almost linearly and was estimated to be 5.0 lm at 60 mA. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates obtained from the measured spectra remained almost constant during the forward-bias current increase from 0.5 mA to 60 mA.

Phosphor-Conversion White Light Emitting Diode Using InGaN Near-Ultraviolet Chip : Semiconductors

A review of recent works on inclusions

Staggered InGaN quantum wells (QWs) are analyzed as improved gain media for laser diodes (LDs) lasing at 440 and 500 nm. The calculation of band structure is based on a 6-band k⋅p method taking into account the valence band mixing, strain effect, and spontaneous and piezoelectric polarizations as well as the carrier screening effect. Staggered InGaN QWs with two-layer and three-layer step-function like In-content InGaN QWs structures are investigated to enhance the optical gain as well as to reduce the threshold current density for LDs emitting at 440 and 500 nm. Our analysis shows that the optical gain is enhanced by 1.5–2.1 times by utilizing the staggered InGaN QW active region emitting at 440 nm, which leads to a reduction of the threshold current density up to 24% as compared to that of the conventional InGaN QW laser. Staggered InGaN QWs with enhanced optical gain shows significantly reduced blue-shift as carrier density increases, which enables nitride QWs with high optical gain in the green spectr...

Optical gain characteristics of staggered InGaN quantum wells lasers

We present analytical expressions for internal electric field and strain in single and multiple quantum wells, incorporating electromechanical coupling, spontaneous polarization, and periodic boundary conditions. Internal fields are typically 2% lower than the fields calculated using an uncoupled model. We point out two possible interpolation routes to calculate the piezoelectric (PZ) constants eij of an alloy from the PZ constants of the constituent materials and show that, for an In0.2Ga0.8N∕GaN quantum well system, the respective internal electric fields differ by 10%. Using an effective-mass model, we explore the effect of the uncertainty in the elastic and PZ constants of GaN on the internal field and optical transitions of InGaN∕GaN quantum wells, and find that the range of published values of eij produces an uncertainty of more than ±20% in the internal field and of more than ±30% in the blueshift in optical transition energy between zero bias and flatband conditions (when the applied field is equa...

Calculation of electric field and optical transitions in InGaN∕GaN quantum wells

Semiconductor quantum dot QD and quantum wire QWI nanostructures have generated considerable experimental and theoretical interest during the last ten years because of the physics associated with the quantum confinement of carriers to less than three dimensions. Devices offer the realistic prospect of improved electronic and optical properties arising from the reduced dimensionality. QD lasers, for example, offer the possibility of reduced threshold currents, reduced temperature sensitivity, and increased differential gain allowing higher-speed operation at reduced power. Improved devices based on QD or QWI nanostructures can be engineered with desirable properties by the control of the materials, band gap, strain, size, shape, and orientation. 1,2

https://epubs.surrey.ac.uk/238/1/fulltext.pdf

Real-space Green's tensors for stress and strain in crystals with cubic anisotropy

The strain interaction energy between a silicon interstitial and a carbon substitutional in a silicon crystal was modeled by a continuum Green’s function method and by atomistic simulation. The interaction energy is proportional to d−3, where d is separation distance between the defects. The pair interaction energy was found to be less than 0.04 meV for d 6 nm increasing to more than about 0.1 meV for d 3 nm. The energies are unlikely to influence the diffusional behavior of the defects except at distances of one or two unit cells. The potential between the point defects is repulsive if they are oriented along the 100 crystal axis, but attractive if they are positioned along 110 or 111 .

Ursula M. E. Christmas

Papers

Calculation of electric field and optical transitions in InGaN∕GaN quantum wells

Real-space Green's tensors for stress and strain in crystals with cubic anisotropy

Elastic interaction energy between a silicon interstitial and a carbon substitutional in a silicon crystal