Surface passivation of germanium by atomic layer deposited Al2O3 nanolayers

Abstract

Surfaces of semiconductors are notorious for the presence of electronic defects such that passivation approaches are required for optimal performance of (opto)electronic devices. For Ge, thin films of Al2O3 prepared by atomic layer deposition (ALD) can induce surface passivation; however, no extensive study on the effect of the Al2O3 process parameters has been reported. In this work we have investigated the influence of the Al2O3 thickness (1–44 nm), substrate temperature (50–350 °C), and post-deposition anneal (in N2, up to 600 °C). We demonstrated that an effective surface recombination velocity as low as 170 cm s−1 can be achieved. The role of the GeOx interlayer as well as the presence of interface charges was addressed and a fixed charge density $${Q}_{\mathrm{f}}=$$ Q f = −(1.8 ± 0.5) × 1012 cm−2 has been found. The similarities and differences between the passivation of Ge and Si surfaces by ALD Al2O3 prepared under the same conditions are discussed. Graphic Abstract

Excellent surface passivation of germanium by a-Si:H/Al2O3 stacks

“…28,[64][65][66] Inspired by the success of Al 2 O 3 for the surface passivation of c-Si surfaces, we investigated in our previous work the surface passivation of Ge by ALD Al 2 O 3 for optoelectronic applications. 67 We found a surface recombination velocity of S eff,max = 170 cm s −1 on p-type Ge (0.2 Ω cm) after optimization of the ALD substrate temperature, film thickness, and post-deposition annealing (PDA) temperature. Moreover, we found a negative fixed charge density of Q f ≈ −2 × 10 12 cm −2 , which contributed to field-effect passivation.…”

“…The latter explains the difference in the Q f value reported in this work and our earlier work. 67 The insertion of a 2.3 nm a-Si:H film between the Ge and the PEALD Al 2 O 3 (blue) appears to have a considerable effect on the Q f ; the fixed charge density increases with more than an order of magnitude from Q f = −0.2 × 10 12 cm −2 up to Q f ≈ −9 × 10 12 cm −2 . The thermal ALD Al 2 O 3 film deposited directly on Ge (orange) yields a negative fixed charge density of about Q f = −3.5 × 10 12 cm −2 .…”

Extracting surface recombination parameters of germanium–dielectric interfaces by corona-lifetime experiments

“…An example of such an experiment is a so-called corona-lifetime experiment. 30,[38][39][40][41] In such an experiment, the semiconductor surface potential is altered by the deposition of atmospheric ionic species [(H 2 O) n H + or CO 3 − ] 42 on the dielectric passivation film via a corona discharge setup. The changes in surface potential result in changes of the surface recombination velocity (S eff ), which are monitored as a function of deposited corona charge density (Q c ) by carrier lifetime measurements.…”

Probing crystallographic orientation-specific carrier lifetimes in epitaxial Ge/AlAs and InGaAs/InP heterostructures

“…The crystallographic plane of a semiconductor material is key to a number of technological importances, such as silicon (Si) based nanoscale fin transistors, where (100) and (110) surfaces were used for ultra-low power CMOS circuit, epitaxial growth, aspect ratio trapping of dislocations for growing epitaxial GaAs films on grooved Si substrates, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] artificial facet-engineered surfaces, and the interfaces of photocatalytic materials 21,22 for enhancing their photocatalytic performances. These man-made or naturally occurring crystal surfaces with microscopic facets would strongly influence their photocatalytic, electronic, and photonic properties.…”