Wei-Chen Yang

Growth mechanisms of plasma-assisted molecular beam epitaxy of green emission InGaN/GaN single quantum wells at high growth temperatures

The results of the growth of thin (∼3 nm) InGaN/GaN single quantum wells (SQWs) with emission wavelengths in the green region by plasma-assisted molecular beam epitaxy are present. An improved two-step growth method using a high growth temperature up to 650 °C is developed to increase the In content of the InGaN SQW to 30% while maintaining a strong luminescence intensity near a wavelength of 506 nm. The indium composition in InGaN/GaN SQW grown under group-III-rich condition increases with increasing growth temperature following the growth model of liquid phase epitaxy. Further increase in the growth temperature to 670 °C does not improve the photoluminescence property of the material due to rapid loss of indium from the surface and, under certain growth conditions, the onset of phase separation.

Semiempirical method of suppressing interference effects in photoluminescence spectra of GaN heterostructures

Interference fringes are generally found in the photoluminescence (PL) spectrum of heterostructures with large refractive index differences between layers and with a smooth interface. To eliminate the interference effects in an air/GaN/InGaN/GaN/Al2O3 structure, the measured interference fringe wavelengths of the PL spectrum are used to deduce the frequency dependent interference function of the system. This interference function is then used to numerically remove interference fringes from the as-measured PL spectrum. This versatile semiempirical method allows the derivation of the true PL spectrum from the measured data, including angular dependent spectra, without complicated calculations or additional measurements.

Influence of Al/Si Codiffusion on Current Gain Deterioration in AlGaN/GaN Single Heterojunction Bipolar Transistors

AlGaN/GaN single heterojunction bipolar transistors (SHBTs) without using regrown emitter junction are demonstrated. Secondary ion mass spectroscopy analysis shows that a severe codiffusion of Al and Si exists in AlGaN/GaN heterostructures grown at 780 °C. The altered composition and doping profiles greatly degrade the common-emitter current gain of AlGaN/GaN HBTs to ≤0.8. A GaN spacer layer is inserted at the emitter-base junction to alleviate this problem. In an AlGaN/GaN HBT structure inserted with a 20 nm unintentionally doped GaN spacer layer, a current gain β about 2 is achieved.

GaN Schottky diodes with single-crystal aluminum barriers grown by plasma-assisted molecular beam epitaxy

GaN-based Schottky barrier diodes (SBDs) with single-crystal Al barriers grown by plasma-assisted molecular beam epitaxy are fabricated. Examined using in-situ reflection high-energy electron diffractions, ex-situ high-resolution x-ray diffractions, and high-resolution transmission electron microscopy, it is determined that epitaxial Al grows with its [111] axis coincident with the [0001] axis of the GaN substrate without rotation. In fabricated SBDs, a 0.2 V barrier height enhancement and 2 orders of magnitude reduction in leakage current are observed in single crystal Al/GaN SBDs compared to conventional thermal deposited Al/GaN SBDs. The strain induced piezoelectric field is determined to be the major source of the observed device performance enhancements.

Design the GaN junction barrier schottky diodes with array p-type pillar

The performance of JBS (P, S) structure within threading dislocations-induced (GaN on PSS~108cm-2) traps and in drift-diffusion simulations, including the critical electric field are studied. As the forward and reverse operation, the pillar-to-pillar of various diode lead to the lower turn-on voltage and high breakdown, respectively. Then, it is important to note that is not punch-through the drift layer to n+-GaN yet because that difference is attributed to whether the intrinsic or extrinsic C-dopants, results in the n--type drift layer or p+-type with bias-dependent deletion region.

Modeling the effect of acceptor-type traps on internal electric field of a GaN-pin device phenomenon

The performance of a pin structure diode fabricated on epitaxial layer on a GaN template using re-growth p-type GaN technology by PAMBE. Experimental results show that relatively forward turn-on voltage and on-resistance are 3.1V and 5mΩ-cm2, respectively. Due to the metal-semiconductor interface has the lower p-ohmic contact. On the contrary, the breakdown voltage of the device operating greater than 800V is observed. Furthermore, the pin structure diode within acceptor-type traps using a two-dimensional simulator as GaN bulk within threading dislocations (about ~108cm-2) was compared to including the electric field different from x and y position. It leads to substantially higher electric field as function of x position between the metal and the p-type GaN when drift layer is not fully depleted.

Directional luminescence control of InGaN/GaN heterostructures using quantum structure lattice arrays

The spontaneous surface luminescence properties of InGaN/GaN quantum structure lattice (QSL) are reported. The QSL consists of a two-dimensional array of InGaN/GaN quantum boxes (QBs) arranged in a rectangular pattern of 200 nm periodicity. The measured angular dependent photoluminescence (PL) spectra show a strong dependence on the in-plane Bragg diffractions between QBs. The maximum PL intensity of the InGaN/GaN QSL array that fulfill the Bragg condition points in the normal direction of the sample surface with a narrow radiation angle of ∼ ±12°. In addition, a small side lobe is also shown at ±40°. For the QSL sample that does not fulfill the Bragg diffraction condition, the radiation pattern shows a conventional cosine distribution. The finite-difference time-domain numerical analysis confirms that the lowest order and higher order Bragg diffractions between QBs determine the main and the small side lobe of the radiation pattern measured in QSLs, respectively.