In this paper, we focused on tuning the emission wavelength of InGaN/GaN multi-quantum wells (MQW) employing
strain-accommodative structures. Generally, the adjustment of emitting wavelength is realized by controlling the
quantum well (QW) thickness and the QW growth temperature, which decides the indium concentration. It needs large
thickness and low temperature to emit long wavelength photons. However, the material quality, electrical and optical
properties will degrade with low growth temperature or wide QW. Meanwhile, the growth of long wavelength LEDs
based on the InGaN material still faces severe difficulties because of the large (11%) lattice mismatch between InN and
GaN and the strong piezoelectric field-induced quantum-confined Stark effect (QCSE) induced by the high strain due to
lattice mismatch. Compared to the conventional LEDs, LEDs with proper strain-accommodative structures not only
increase the emitting wavelength but also reduce the strain in InGaN well. It provides an alternative approach to tune the
Two types of strain-accommodative structures are inserted between n-GaN and the multi-quantum wells: one is short
period super lattices (SPSL) consisted of 15 period of the 1-nm-thick InGaN well and the 2-nm-thick GaN barrier , and
the other is 45nm InxGa1-xN (x=0.07-0.09). The samples with strain-accommodative structures demonstrate that: firstly
the two structures would efficiently increase the wavelength, which should be attributed to the relief of strain in the
InGaN/GaN MQWs. The wavelengths of the two structures in the electroluminescence measurement were 561.6nm and
531nm, respectively. It is longer than that of the control sample (511.8nm). Secondly; the structures can weaken the
QSCE. When the current increased from 3mA to 20mA during the electroluminescence measurement, the peak
wavelength blue-shift were 5.1nm and 3.1nm, respectively. It is smaller than that of the control sample (7.4nm).
The earlier astable multivibrator formed by silicon tunnel diode has the disadvantage of low speed and non-modulation.
NDRHBT is a novel type of HBT with NDR characteristics and high speed. Its NDR characteristics can be modulated by
the base voltage VBE or base current IB. So the astable multivibrator formed by NDRHBT has the advantage of high
speed, high frequency, bistability, and frequency modulation by VBE or IB. Thus, it can be applied widely in high
frequency oscillation circuits and high speed-digital circuits.
In this paper, it is demonstrated that the frequency of the astable multivibrator can be modulated by base voltage VBE.
The experimental result shows that the frequency of time interval between two adjacent pulses f1 varies from 7×104Hz
down to 2.5×104Hz as VBE changes from 4.5V to 6.5V and exhibits near a linear relationship. So it is can be used as an
efficient voltage controlled frequency modulator for pulse signal in high speed digital circuits.
In this paper, it is reported that the design and fabrication of high-brightness and high-power
InGaAlP single-side red LED with electrodes which are interdigitated with the fingers.
High-brightness and high-power InGaAlP LED is a new kind of visible light LED developed in
recent years, which is driven by large current capacity, high luminous efficiency and excellent heat
resistance. It has been used in various fields, such as large area displays, traffic lights, brake lights
and so on. As compared with the conventional double-side LED, the single-side LED is more
flexible to integrate with other devices and its fabrication is simplified.
The size of chip is 1mm2. The fabrication of single-side LED, essentially, is the same as
conventional LED, involving photolithography, PECVD SiO2, wet etching, evaporating, lift off
and rapid thermal annealing using four masks. To control the widths of mesa and N electrode
precisely, the selecting etch technique has been adopted, using HCL: H2O:H2O2 as the InGaAlP
I-V characteristics, light emission spectrum, luminous flux, luminous intensity and luminous
efficiency of this LED have been measured. The characteristics are obtained with turn-on voltage
of 1.5V and forward current of 400mA at its forward voltage of 3V. The peak wavelength is
635nm, which corresponds to red light, and the Full Width of Half Maximum is 16.4nm at
injection current of 350mA. The luminous intensity is 830 mcd. The color coordinates is x=0.6943,
y=0.3056 and the color index is 18.4. So we will conclude that the high-brightness and
high-power InGaAlP single-side red LED will become new focus in both scientific research and
industrial investment for its wide application.