1. 4H–SiC ultraviolet avalanche hotodetectors with low breakdown voltage and high gain Huili Zhu, Xiaping Chen, Jiafa Cai, Zhengyun Wu YC Chiang

2. Outline Introduction Experiments Results and discussion Conclusions References

3. Introduction 4H–SiC is an attractive material for optical detection in the short-wavelength UV regime owing to its wide bandgap, high thermal conductivity and high critical electric field. SAM-structure has separate high-field multiplication and absorption regions, optimizing the thicknesses and doping concentrations of absorption and multiplication layers,the problem occurred at p–n and p–i–n structure APDs will be resolved.

4. Experiments Fig. 1. Schematic cross-section of the 4H–SiC SAM-APD. type p+p+ nn-n- 濃度 及 厚度 1x10 15 / cm 3 and 1um <4x10 17 / cm 3 and 0.25um 5x10 19 /c m 3 and 0.3 作用倍增區 吸收區 及 穿隧區

5. Results and discussion Fig. 2. I–V characteristics and gain of 4H–SiC APD. 27.5V 1.8x10 4 55

6. Results and discussion The punch-through vlotage ~27.5V Punch-through is the condition at which the edge of the depletion region reaches the absorption layer and photo-generated carriers can be pulled across the barrier at the homointerface

7. Results and discussion η is the ideality factor k is Boltzmann’ constant q is the electron charge T is the absolute temperature Js is the saturation current

8. Results and discussion Fig. 3. Typical I–V characteristics of 4H–SiC APD. Inset: the fitting of the linear region of forward I–V curves.

9. Results and discussion Fig. 4. Spectral responsivitives of 4H–SiC APD measured under various biases. 35.8% 93% 0.078 0.203

10. Results and discussion q = 電荷量 η Q = 量子效率 H = 普郎克常數 υ = radition frequency R 0 = 動態電阻 A =detector Area K = 波茲曼常數 T = 絕對溫度

11. Results and discussion 由 Fig 3 得到在零偏壓時,R 0 A~3.2*10 7 Ω cm 2 經過計算得到 D*~3.1 x 10 13 cmHz 1/2 W -1

12. Results and discussion

13. Conclusions The dark current density was below 10 pA when the reverse bias below 27.5 V. In addition, the dark current increased with increasing reverse bias,which might be due to the defects of passivation layer resulting in higher leakage current. The UV/visible ratio were larger than 10 3 which showed the samples had excellent performance for ultraviolet light detection. When the reverse bias was larger than 35 V, the avalanche multiplication was observed.

14. References SiC 之簡介 http://www.ecn.purdue.edu/WBG/Introduc tion/Index.html http://www.ecn.purdue.edu/WBG/Introduc tion/Index.html 光電元件導論, 第二版, 劉博文著 SEMICONDUCTOR DEVICES Physics and Technology,2 nd Edition,S.M. Sze