InAs Infrared Photodiodes

Abstract

Advances in Photodiodes 428At the same time these PDs are characterized by rather low values of the differential resistance -area product R 0 A at room temperature. This seems to be the main reason that InAs infrared photodetectors operate in sub-BLIP regime (Rogalsky, 1995). Further improvement in their performance is possible with a decrease in dark current and supression of Auger recombination. Preparation of photodiodes and experimental techniquesHomojunction PDs were prepared by short-term (20-30 min) diffusion of Cd into n-InAs substrates at T=875 K. The substrates of n-type conductivity were cut from single-crystal ingots grown in joint-stock company "Pure metals plant" (Svetlovodsk, Ukraine). The damaged surface layers were removed by using dynamic chemical-mechanical polishing in 2% Br 2 -CH 3 OH solution. Their structural quality was controlled by X-ray diffraction method. In the chemically polished substrates the rocking curves half-width was 25-27 '' . Electrical parameters were controlled by van der Pauw technique at 295 K. The carrier concentration and mobility were found to be n=(2÷3)×10 16 cm -3 and µ n =(2÷2.5)×10 4 cm 2 /V×s, respectively. The density of dislocations was in the range (2÷4)×10 4 cm 2 . The substrates with the diffused p-type layer had mirror-like surfaces free of structural damages such as inclusions of impurity atoms. They were characterized by the rocking curve halfwidth of 32-35 '' . Typical profiles of Cd atoms in a substrate are shown in Fig.1. As seen, at low values of depth x they can be approximated by two exponential dependences (shown by solid lines in Fig. 1). Similar profiles of impurity atoms were previously observed in GaAs (Grigor'ev & Kudykina, 1997) and explained by generation of non-equilibrium vacancies at the substrate's surface. In such a case, an impyrity profile is determined by distribution of vacancies under the surface. The junction depth was determined from the probe thermo-emf measurements during careful chemical etching of diffused layers. Mesa structures were prepared on (111)A side of substrates by chemical etching in 2% Br 2 -HBr solution. In order to eleiminate the surface leakage current mesas were passivated by etching in HNO 3 -based solution followed by deposition of anode oxide doped with fluorine with thickness of 0.3 m. After passivation they were covered by thin layer of ZnTe thermally deposited in a vacuum chamber at temperature 150 o C. The heterojunction p + -InAsSbP/n-InAs PDs were prepared by LPE technique in IOFFE Physico-Technical Institute, St.-Petersbur Russia (Zotova, 1991;Matveev, 1997;Matveev, 2002). For this purpose, lattice matched InAsSbP epitaxial layers of approximately 3 μm thickness were grown on (111)B surfaces of InAs substrates. The quaternary InAsSbP compound had energy gap of 0.43 eV at T = 297 K. The epilayers were doped to about 10 18 cm -3 by addition of Zn to the melt. The substrates were n-type single crystals with electron concentration n=(2÷3)×10 16 cm -3 . In homojunction and heterojunction PDs mesa struc...

Carrier transport mechanisms in reverse biased InSb p-n junctions

“…The excess tunneling current in the forward-biased InAs photodiodes was satisfactorily explained in terms of inhomogeneous junction that contains local areas with a much higher concentration of defects [26]. The local inhomogeneities may be related to dislocations or other extended defects that release excess strains in semiconductors.…”

“…A model of trap-assisted tunneling (TAT) current has been developed in [24,25]. Based on this model experimental data were satisfactorily explained in Cd x Hg 1−x Te (x = 0.2…0.3) [25] and InAs infrared photodiodes [26].…”

“…This means that another model of tunneling current should be invoked to interpret experimental data correctly. In a number of published papers [20][21][22][23][24][25][26], various models of the tunneling current in the reverse biased diodes were developed. For instance, the interband tunneling current associated with dislocations has been analyzed in [20][21][22].…”

Carrier transport mechanisms in InSb diffusion p-n junctions

“…Since the thickness of the depletion layer W 0 decreases from 1.2 m at 77 K to 1.0 m at 134 K (see Table), the interband tunneling cannot be dominant at rather low bias voltages |U| ≤ ±U D . Therefore, it is most likely that tunneling occurs through deep defect states localized in the depletion layer [22][23][24][25]. Several models of tunneling current in infrared photodiodes were proposed in the literature [1,20,22,23].…”

“…For instance, in the reverse-biased HgCdTe photodiodes, the soft breakdown was explained by the trap-assisted tunneling mechanism [22,23]. However, as in the case of InAs p-n junctions [25], investigated InSb junctions were found to be substantially influenced by ultrasonic treatment. So, to explain experimental results at forward and reverse biases, the model of tunneling current through dislocations was chosen [24].…”