Barrier Photodetectors for High Sensitivity and High Operating Temperature Infrared Sensors

Transcription

1 Barrier Photodetectors for High Sensitivity and High Operating Temperature Infrared Sensors Philip Klipstein

2 General Review of Barrier Detectors 1) Higher operating temperature, T OP 2) Higher signal to noise at low T OP 3) Simple 2-color architecture 4) Simplification of processing and passivation Standard Diode Barrier diode SPIE March

3 Timeline 1983: Anthony White (UK): patent of barrier devices in MCT: US 4,679, : P C Klipstein, patent of barrier devices in InAsSb and superlattice: WO 2005/ A1 2006: Maimon and Wicks, Appl. Phys. Lett. 89, Coined the name: nbn First nbn fabrication in InAs 2007: U of New Mexico, Appl. Phys. Lett91, First nbn fabrication in Superlattice SPIE March

4 BIPOLAR X Bn Detector Family - No Depletion in NARROW bandgap absorber - Holes free to move from absorber to contact p-b-n UNIPOLAR n-b-n BIPOLAR UNIPOLAR C p -B-n C n -B-n SPIE March

5 Standard Diode: NARROW bandgap is depleted GR process S-R-H trap (G-R centre) Diffusion process E G IDiffusion IGR ~ ~ EG kbt e EG 2kBT e I = I + I Diffusion GR 77K L n L dep L p Log I E /k /kslopes G B slopes I MWIR (λ C ~4µ) at 77K: 1 N L τ E /2k GR D Dep p0 4 5 ~ ~ IDiffusion 2 ni L τ p n0 SPIE / T 19 March G B

6 XBn has no depletion in narrow bandgap S/C XBn has negligible G-R current Log I I STD XBn (high temperature) Dark Current Arrhenius plot Standard diode XBn (high sensitivity) XBn Device only has an advantage below T 0 T 0 1 / T I STD < I photo SPIE March

7 E C E (p) F E V GaSb AlSbAs V bias MWIR CBn detector Room Temperature Bandgap (ev) GaP Si AlP GaAs AlAs Ge InP AlSb GaSb InAs Indirect Gap Direct Gap InSb Lattice Constant (nm) Room Temperature Wavelength (microns) InAsSb E C E F(n) SPIE March E V i) Optical behaviour like narrow gap diode ii) Electrical behaviour like wide gap diode

8 log 10 I J GR Estimation of crossover temperature, T 0 Ldep NvNc = 2 τ τ InSb p 0 n /T ( K -1 ) e T0(K) k T 50 E G B J GR (T 0 )= J diff (T 0 ) τ n0 ~300nS D P ~32cm 2 /s (τ p0 ~500nS) T 0 ~130K N=2e16 N=2e Bandgap (ev) SPIE March J Diff ~ InAs 0.91 Sb 0.09 T 0 ~170K NC N N D V L τ diff p p 0 e E B G k T V.P. Astakhov et al. Pis ma Zh Tekh Fiz 18, 1 (1992) InAs

9 Estimation of XBn Operating Temperature, T 0P Temperature (K) λ C = 4.2µ (E G =0.3eV) T 0 1.E+14 1.E+15 1.E+16 1.E+17 N D (cm -3 ) T OP: BLIP/10 (f/3;qe=0.7) InAs 0.91 Sb 0.09 BLIP/10: J diff (T OP )= J photo /10 T OP < T 0, so barrier detector works HOTTER than standard detector Real T OP ~ 150K is feasible for large N D Barrier detector tolerates large N D because depletion width is independent of N D (determined by barrier width) and bias SPIE March

10 C p -B-n AlSb As 1-x x Bias Range E C p-type GaSb V bias =V MAX E C V bias <V MAX E (p) F E V ξ V bias InAs Sb 1-z z E (n) F E C E V E F(p) E V < 3kT OP V bias E (n) F E C E V No G-R current = higher T OP SPIE March

11 C p -B-n Barrier Doping E C barrier p-type GaSb AlSb As 1-x x Flat bands, in InAsSb p-type barrier Bent bands, in InAsSb E (p) F E V ξ V bias InAs Sb 1-z z E (n) F E C E V Hole accumulation layer V BIAS Depletion in absorbing layer = lower T OP SPIE March

12 Type II SL CBn detectors Al Ga Sb As 1-x x 1-y y SL( ) λ 1 SL( ) λ 2 E F,L V bias E F (n) λ 1 λ 2 E F,R C p -B-n C n -B-n (2 colour) SPIE March

13 Type II SL CBn detectors Al Ga Sb As 1-x x 1-y y SL( ) λ 1 SL( ) λ 2 E F,R E F,L V bias E F (n) λ 1 λ 2 C p -B-n C n -B-n (2 colour) SPIE March

14 Processing of XBn Detector B C p n-active layer Etch stop B C p n-active layer Cap B Metal C p n-active layer I Metal -Barrier acts a bit like overgrown passivation layer -Standard LWIR FPAs are hard to passivate XBn could be a good alternative passivation solution SPIE March

15 C p -B-n Limits on Barrier width and height t. emission GaSb E C ~1.0eV n-b-n t. emission E C ~2.1eV η V bias tunneling InAs Sb InAsSb tunneling InAs Sb InAsSb I TE, I tunn < I photo (f/8, QE=0.7) gives Thermionic emission: E C >0.4eV (based on Richardson Formula) Tunneling: Barrier Thickness > 300Å (based on 2-band k.p calculation) SPIE March

16 Conclusions 1. XBn Detectors come as CBn, pbn, nbn, etc. 2. No depletion in absorbing layer and no G-R current 3. Anticipated Advantages for MW and LW i) HOTTER than a standard photodiode (MWIR) ii) LESS NOISE at lower T OP (MWIR) iii) EASIER to passivate (LWIR) iv) 2 color (including MW/LW) is simple in nbn configuration v) All proposed designs grown on GaSb substrates 4. XBn detector design for better performance : barrier and high doping in absorbing layer SPIE March