Electro Optical Characterisation of Short Wavelength Semiconductor ...

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Data Analysis can be due to the suboptimal metal contact brought on the structures. The spectra show a multimode lasing in most of the cases. The diffrent peaks are energetically very close to each other though. Fig. 4.11 shows a far field picture of one ZnSe laser device taken by a regular digital camera. A white piece of paper was kept in font of the laser diode. The far field of the laser can be captured this way. The sharp vertical light line is the actual sign of lasing. 4.2 GaN Devices Figure 4.11: Far field of a ZnSe laser diode Fig. 4.12 shows the principle assembly of the homoepitaxial GaN laser diodes grown in Bremen. Four different series of structures have been investigated. Three series, g0937, g0938 and g0942, are almost the same except for the n-doped AlGaN cladding layer thickness. This is 1.5µm for g0937, 2µm for g0938 and 1µm for g0942. The rest of the structure is exactly the same grown as depicted in Fig. 4.12 for all three named crystals. They are grown on an LED-grade GaN substrate. Generally there are three different grades possible for the GaN substrates which are LED-, transistor- and laser-grade with 10 −8 , 10 −7 and 10 −6 defects/cm 2 respectively. Thus, the g0975 series grown on a transistor-grade substare are qualitatively better than the g0937, g0938 and g0942 series. The g0975 is besides grown as a standard structure, i.e. an n-doped AlGaN cladding layer of thickness 0.5µm. The g0975 is processed in three different ridge widths (2µm, 6µm and 10µm). Each width is then processed ones as a planar structure as well as a shallow ridge and a deep ridge. As it can be obtained from Figs. 4.12 and 4.13 the shallow ridge is the case when the semiconductor material beside the quantum well is etched down to the undoped GaN wave guide. Whereas in case of a deep ridge the material is etched down to the middle of the Si-doped GaN wave guide, thus through the active region (compare to 2.2.2). 40
GaN:Mg contact layer GaN Devices MOVPE: High Mg-doped GaN-contact layer, d=20nm MOVPE: GaN:Mg, d=80nm MOVPE: Al 0,08 Ga 0,92 N:Mg cladding, d=500nm Electron blocking layer: Al 0,2 Ga 0,8 N, d=40nm Undoped GaN waveguide, d=100nm 3x In 0,09 Ga 0,91 N/GaN quantum well, each ~10nm MOVPE: Si-doped GaN waveguide, d=100nm MOVPE: Al 0,1 Ga 0,9 N:Si cladding, d=500-2000 nm MOVPE: GaN:Si, d=500 nm HVPE: (Lumilog) n-doped GaN substrate d=300µm (LED-, transistor- or laser-grade) Figure 4.12: Principle assembly of a III-V laser diode made in Bremen Planar structure Shallow ridge Deep Ridge – etched through quantum well Figure 4.13: Different ridge depths [55] 41
Page 1: University of Bremen Technical Univ
Page 4 and 5: Preface ing the characterisation me
Page 6 and 7: CONTENTS 4.2.1 Characterisation of
Page 8 and 9: Basic Concepts Semiconductor lasers
Page 10 and 11: Basic Concepts many problems appear
Page 12 and 13: Basic Concepts 1.2.2 Light in Cryst
Page 14 and 15: Basic Concepts which by using 1.6 c
Page 16 and 17: Basic Concepts Eq. 1.19 delivers di
Page 18 and 19: Basic Concepts light below the mate
Page 20 and 21: Developing Laser Diodes Metalorgani
Page 22 and 23: Developing Laser Diodes 18 4. Lift
Page 25 and 26: Chapter 3 Characterisation Life can
Page 27 and 28: 3.1.3 SEM & FIB Opto-Electrical Cha
Page 29 and 30: voltmeter current source + − 000
Page 31: current source + − 000 111 000 11
Page 34 and 35: Data Analysis As it can be seen the
Page 36 and 37: Data Analysis Output Light Power [W
Page 38 and 39: Data Analysis trometer. This could
Page 40 and 41: Data Analysis Current [mA] 400 300
Page 42 and 43: Data Analysis Following the trend o
Page 46 and 47: Data Analysis It is worth mentionin
Page 48 and 49: Data Analysis for the whole devices
Page 50 and 51: Data Analysis Figure 4.18: Optical
Page 52 and 53: Data Analysis current density 1.75
Page 54 and 55: Data Analysis levels of the quantis
Page 57 and 58: Chapter 5 Summary and Outlook Great
Page 59: Appendix A Electrical Sources & Mea
Page 62 and 63: ZnSe threshold current density valu
Page 65 and 66: Bibliography [1] N. G. Basov, O. N.
Page 67: BIBLIOGRAPHY [56] G. Snider, 1D Poi

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