Optical measurement of carrier concentration profile in n‐type semiconducting GaAs substrate

Abstract

The light absorption below the fundamental energy gap in n‐type GaAs has been investigated precisely. It is experimentally confirmed that there are the three different mechanisms: (a) the enhancement of fundamental absoption due to the shrinkage of energy gap and band filling by doping Si atoms, (b) deep‐level (EL2) absorption, and (c) free‐carrier absorption. It is found that the transmittance measurement at the wavelength longer than about 1000 nm in the free‐carrier absorption region is more useful and direct, compared with that near the fundamental absorption region from 900 nm to 950 nm, precisely to determine the carrier concentration in n‐type GaAs. The two‐dimensional profile of carrier concentration in a VB‐grown 3 ϕ GaAs substrate is measured in high spatial resolution with the short time less than 5 seconds by using a sophisticated near‐infrared transmittance‐measuring equipment. The absolute amount and homogeneity of carrier concentration can be assessed in the range from 0.3 to 3 × 1018 cm–3. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Homogeneity assessment of large‐diameter III‐V compound semiconductor substrates by near‐infrared transmittance measurement

“…2 Light absorption below the fundamental energy gap Figure 1 shows the wavelength dependence of the absorption coefficient measured in undoped and Sidoped GaAs substrates [9]. It is clearly seen in Fig.…”

“…where α FG (λ), α EL2 (λ), and α FC (λ) are the absorption coefficients originating from the different mechanisms: (a) enhancement of fundamental absorption due to shrinkage of the energy gap and band filling by doping Si as impurity atom, (b) free-carrier absorption, and (c) deep-level (EL2) absorption [9]. In InP, the same description may be applied except for taking the Fe-level in semi-insulating InP instead of deep levels (EL2) in semi-insulating GaAs.…”

“…However, there was a technical difficulty in measuring the carrier concentration distribution over an area more than 70 mm (about 3-inches) in diameter. By developing near-infrared transmittance (NIRT) mapping equipment, we have succeeded not only in assessing the homogeneity of semiconducting InP substrates with diameter up to 4 inches [7], but also in evaluating the carrier concentration distribution in n-type InP and GaAs substrates [8,9]. In the present paper, we will present NIRT maps for the homogeneity assessment in III- V compound semiconductor substrates with diameter up to 6 inches after investigating the light absorption mechanisms below the fundamental energy gap.…”

The fine structure of electron irradiation induced EL2-like defects in n-GaAs

“…8,9 In some instances, the defect traps electrons when they are accelerated into semi-insulating regions and may create regions of fixed trap charge that can ruin devices. 10 On the other hand, it can be deliberately introduced to increase resistivity of bulk GaAs so as to lower substrate capacitance and allow high frequency operation of devices.…”