長程光纖通訊光源材料 InGaAsN 之特性介紹與近代發展 Reporter: 陳秀芬 Adviser: 郭艷光 博士 Date: 2004/01/06 92 學年度第一學期半導體雷射期末報告

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 2 Outline Introduction Comparison of InGaAsN, AlGaInAs, and InGaAsP Physics of InGaAsN Modern research on InGaAsN Conclusion

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 3 Introduction Long-wavelength (1.3/1.55  m) quantum-well lasers based upon InGaAsP materials are widely used in optical communications applications, but the temperature dependence of these lasers remains an issue that limits their performance at high temperature. Thus, in recent years, different material systems have been sought to improve the active region performance, including AlGaInAs and InGaAsN.

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 4 Comparison of InGaAsN, AlGaInAs, and InGaAsP InGaAsNAlGaInAsInGaAsP Characteristic Temperature, T 0 (K) The rate of the gain peak shift (nm/K) Band offset ratio (  E c /  E v ) m e / m m hh / m Material Property

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 5 Physics of InGaAsN --- Composition & GaAs substrate GaN (~4.5Å) and GaAs (5.65Å) have very different lattice constants, which means that GaAsN layers grown on a GaAs substrate should be highly strained. By adding indium we can grow InGaAsN layer completely lattice matched to GaAs substrate.  VCSEL When substituting just 1% N for As in GaAs, the band- gap energy decreases from 1.42 to 1.25 eV at room temperature, although the GaN band-gap energy is much higher ~3.43 eV. This is due to the coupling of a nitrogen level with the  conduction band.

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 6 Physics of InGaAsN --- Effective mass Because the nitrogen states and the electron states in the conduction band repulse each other, electron effective mass of InGaAsN is about 0.08 m 0 and is about 1.6 times that of AlGaInAs. These values of effective masses result in the higher transparency carrier density of InGaAsN. However, the large electron effective mass improves the matching between the density of states of the conduction band and that of the valence band (  v ~ 1.4  c ), so that the differential gain (dg/dn) is enhanced.  High-speed modulation

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 7 Modern research on InGaAsN Paper1-APL2003 Improved photoluminescence of InGaAsN-(In)GaAsP quantum well by organometallic vapor phase epitaxy using growth pause annealing Paper2-APL1999 Ultrafast (GaIn)(NAs)/GaAs vertical-cavity surface-emitting laser for the 1.3  m wavelength regime Paper3-EL2000 Room temperature continuous wave InGaAsN quantum well vertical-cavity laser emitting at 1.3  m.

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 8 Paper1-Active region scheme Sample ASample B & C

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 9 Photoluminescence spectra of In 0.4 Ga 0.6 As N QW with GaAs and GaAs 0.85 P 0.15 direct barriers Without employing a growth pause before and after the InGaAsN QW, no luminescence intensity was measured from structures with direct barriers of GaAs 0.85 P 0.15.

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 10 The luminescence intensity and the peak emission wavelength of InGaAsN QW with 1.62 eV InGaAsP direct barriers The photoluminescence of the InGaAsN QW with InGaAsP direct barriers shows the trend of increasing luminescence intensity as the pause time is increased.

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 11 The FWHM of the optical luminescence spectra for InGaAsN QW with 1.62 eV InGaAsP direct barriers This improvement is also accompanied by a reduction in the full width half maximum FWHM.

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 12 Paper2-Scheme of structure The 1.3  m VCSEL are designed and grown by metal-organic vapor- phase epitaxy (MOVPE). They use optical excitation with a mode- locked Ti:sapphire laser (0.92  m).

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 13 Intensity of the time-integrated emission as a function of the internal excitation density The threshold excitation densities are between 1.6 and 2.0 kW/cm 2 in the center and near the edge of the (GaIn)(NAs) sample. The threshold value of the ( GaIn)(NAs) VCSEL is smaller than the threshold of the (GaIn)As/Ga(PAs) VCSEL (4.5 kW/cm 2 ). Center: 1.6 kW/cm 2 Edge: 2.0 kW/cm  I th 0.8  I th

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 14 The peak delay time and the peak width of the VCSEL emission after excitation The peak delay time after the excitation and the full-width at half- maximum (FWHM) of the peak decrease with increasing excitation density. The fastest dynamics is measured at an internal excitation density of 13.4 kW/cm 2, with a peak delay time of 15.5 ps and a peak width of 10.5 ps kW/cm 2

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 15 Paper3-Scheme of structure The VCSEL are grown on GaAs substrates using molecular beam epitaxy (MBE). They use two relatively low- doped n-type mirrors to reduce the free carrier absorption.

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 16 Laser characteristics from 4.5  4.5  m 2 aperture at 20 ℃ The threshold current of the InGaAsN VCSEL is 1.95 mA.

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 17 Lasing spectrum of InGaAsN VCSEL The figure shows the single transverse mode lasing spectrum at 1294 nm with 28 dB. Singlemode output power of 60  W is obtained at 20 ℃.

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 18 Conclusion(1) The advantage of InGaAsN: 1. High characteristic temperature ~ 120K 2. Large band offset ratio ~ Lattice-matched substrate – GaAs 4. Larger differential gain (dg/dn) The disadvantage of InGaAsN: 1. Heavier electron effective mass 2. Higher transparency carrier density 3. Low output power of InGaAsN VCSEL

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 19 Conclusion(2) InGaAsN is found to be advantageous for temperature-insensitive, high-speed modulation applications at 1.3  m. It is especially appropriate for VCSELs that require slow redshift of gain with respect to the temperature. With further improvements in the mirrors, cavity, and quantum well design, we can expect that appropriate long wavelength performance will be achieved.

2004/01/06 國立彰化師範大學藍光實驗室 陳秀芬 20 Thanks for your attention!!