THE HYDROGENATED AMORPHOUS-SILICON REACH-THROUGH AVALANCHE PHOTODIODES (A-SI-H RAPDS)

The RAPD structure is adopted to improve the electrical and optical performance of the photosensing device made of a-Si: H. Both the electron-injection n+−i−δp−i−p+ and hole-injection p+−i−δn− i−n+ a−Si: H RAPD’s are fabricated on the ITO-coated glass substrates by plasma enhanced chemical vapor deposition (PECVD) system. The photocurrent multiplication method is employed to study the multiplication factors and the impact ionization coefficients of the a-Si:H RAPD’s. Since the electron-injection models have better performance, the relationships between the device dimensions and characteristics, such as I- V curves, optical gains, impact ionization rates, and excess noise factors are further studied and presented. An optical gain of 380 can be obtained under a 5 μW He-Ne laser input light power and at a reverse-bias voltage of 14.5 V. The excess noise factor is 6.47 at a multiplication of 33.46. The dynamic rise time of 1 μs has been observed under a 1.8 kΩ load resistance. The hole and electron impact ionization rates (β and α) can be expressed empirically by β(E) = 9.87 × 104 exp (−1.36 × 106/E) cm−1 and α(E) = 6.34 × 105 exp (−3.16 × 105/E) cm−1 for electric field E ranging from 5 × 105 to 3.5 × 106 V/cm, respectively. Based on the results of this paper, the a-Si:H RAPD would be a promising a-Si: H device for the photosensing applications. © 1990 IEEE