Lasers: Structures and Properties

Presentation on theme: "Lasers: Structures and Properties"— Presentation transcript:

1 Lasers: Structures and Properties
Prepared based on Semiconductor optoelectronic devices, by P. Bhattacharya

2 Junction Laser Operation Principles
Semiconductor optoelectronic devices, by P. Bhattacharya

3 Semiconductor optoelectronic devices, by P. Bhattacharya

4 Semiconductor optoelectronic devices, by P. Bhattacharya

5 Threshold current density
* For linear gain/current relationship, the dependence of Jth on Lc is, p.279 Semiconductor optoelectronic devices, by P. Bhattacharya

6 Semiconductor optoelectronic devices, by P. Bhattacharya

7 Laser Properties Minimization of the threshold current
Reducing active layer thickness, d Increasing internal quantum efficiency, Increasing the differential gain Reducing the cavity and mirror losses d Semiconductor Optoelectronic Devices pp 참조

8 Laser Properties Characteristic temperature, T0
constant Characteristic temperature, T0 레이저 다이오드의 열 특성 평가를 위하여 최대구동 온도를 측정 온도가 증가함에 따라 Itho는 증가하고, 어느 온도 이상에서는 광 전류의 특성 곡선이 직선 형태에서 곡선 형태로 변화하는 모습을 띤다. 70 ℃를 경계로 하여 기울기의 변화 25 ~ 70 ℃ 영역 : 156 K 70 ~ 100 ℃ 영역 : 73 K 온도 영역에 따라 To 가 다른 값을 가지고 온도가 상승할수록 작은 To 값을 가진다. 광구속 영역과 P 클래드 영역의 작은 전도대 에너지 차이 때문에 누설 전류가 고온에서는 빠르게 증가하기 때문. Ref) 김동환, 장준호, 유태경, 전자공학회, 1998

9 1 2 1 2 Semiconductor optoelectronic devices, by P. Bhattacharya

10 3 1 3 Semiconductor optoelectronic devices, by P. Bhattacharya

11 Laser Properties External quantum efficiency
*The optical power output into the modal volume due to a current J (Jth) , A : Junction area *The power coupled out through the cleaved facets as useful laser output and overcome losses *Differential quantum efficiency is defined as the increase in light output due to an increase in drive current Semiconductor optoelectronic devices, by P. Bhattacharya

12 Figure 7.8 Light-current characteristics of an etched mesa buried hetero- structure laser at different temperatures (from G. P. Agrawal and N. K. Dutta , Long wavelength Semiconductor Lasers, Ban Nostrand Reinhold , New Reprinted by permission of AT&T Bell Laboratories Semiconductor optoelectronic devices, by P. Bhattacharya

13 7.3 Heterojunction Lasers
Semiconductor optoelectronic devices, by P. Bhattacharya

14 Semiconductor optoelectronic devices, by P. Bhattacharya

15 Transverse dimension improvement & kink
Semiconductor optoelectronic devices, by P. Bhattacharya