The United States University developed a monolithic integrated three LED future will include other different color combinations

InGaN technology and existing manufacturing facilities based on strain engineering can provide a feasible method for the micro display.

Indium gallium nitride (InGaN) based on the engineering strain quantum well, the University of Michigan has developed a monolithic integrated amber - Green - blue LED (Figure 1). The engineering strain is achieved by etching nanorods with different diameters.

Figure 1. LED nano column array diameter from top to bottom manufacture schematic diagram

The researchers hope that the future can be used 635nm photoluminescence quantum wells to produce red green blue LED, provide a feasible method for the micro display pixel based on LED. Other potential applications include lighting, biosensors and cytogenetics.

In addition to the National Science Foundation (NSF) support, Samsung also provides support for the manufacturing and equipment design. The researchers hope to develop multi chip level LED platform based on the existing manufacturing infrastructure.

Materials grown by metal organic chemical vapor deposition (MOCVD) growth in the 2 inch non patterned sapphire. A light emitting active region consists of 5 2.5nm InGaN wells, separated by 12NM GaN gate. The electron barrier layer and p- contact layer is composed of AlGaN 20nm (p-Al0.2Ga0.8N) and 150nm p-GaN.

The use of electron beam lithography of nano column forming processing, etching mixed with nickel mask dry wet method. Most of the inductively coupled plasma etching is dry, wet etching stage for the realization of the final diameter, and the removal of a dry etching step damage. The etching depth is about 300nm. In the whole manufacturing process, to protect the etching mask, the purpose is to protect the surface of p-GaN.

In the 50nm silicon nitride by plasma enhanced chemical vapor deposition (PECVD) after the formation of the structure with spin on glass, N and p-GaN in electrical isolation.

The structure after the formation of the dry etch back, to expose the tip of the column. Remove the mask material with nickel nitrate solution. P contact the Ni / Au metal thermal annealing in the air.

Performance of electrical equipment in the reverse bias voltage of 5V shows per pixel about 3x10-7A low leakage. Low leakage due to two factors - Flat quantum well provides a low current crowding effect, as well as by the strain caused by the carrier to the nanometer column central limit. Due to the decline in risk effect caused by large current density in nano column narrow, can be improved by reducing the strain, thus reducing the quantum confinement "caused by the electric field induced charge polarization chemical bond III- nitride in the stark effect".

The pixels with different diameters, a different color column (Figure 2). With the increase of the diameter, long wavelength, greater changes. The researchers will change due to the change of quantum well thickness on wafer.

Figure 2. (a) obtained from nano column and thin film LED 50nm, 100nm and 800nm pixel diameter blue (487nm), green (512nm), orange (575nm) and amber (600nm) electric light photoluminescence spectra at room temperature. (b) optical wavelength using one-dimensional stress relaxation theory should be reached. (c) a variety of applied bias voltage under the peak position.

With the increase of voltage and current injection, narrow nanotubes more relaxed also showed less wavelength blue shift. The diameter of 800nm nanorod pixel blue shift between 2.8V and 4V for 40nm. Thanks to the team selection pressure well depends on the strain field.

The team through the pulse frequency modulation fixed bias voltage and intensity change, thus to stabilize the output wavelength of pixels. Through this test shows that all the pixels are given stable wavelength and relative luminescent intensity, and the pulse duty ratio shows almost linear change. The pulse width is 400 s. The pulse frequency between 200Hz and 2000Hz changes. (compiled: LED James)

LED more information, please click on the LED network or the WeChat public account (cnledw2013).