Experimental observations bearing on density-of-states effective masses and on the intrinsic concentration in silicon are reviewed and correlated. These indicate effective masses to be temperature and energy dependent. The valence band structure as determined by Kane is used to calculate the temperature and donor density dependence of hole effective mass. A first order approximation to the explicit temperature variation of both hole and electron effective masses is made using the measured temperature dependence of the energy gap. When these temperature-dependent effective masses are substituted into the theoretical expression for intrinsic concentration the agreement with reported measurements of ni is within the limits of error. Density-of-states effective masses at 300°K are found to be m e ∗ = 1·18 and m h ∗ = 0·81 in contrast to the generally used 4·2°K values of m e ∗ = 1·06 and m h ∗ = 0·59 .

Effective mass and intrinsic concentration in silicon

Free carrier absorption in heavily doped layers reduces the useful photon flux in the photoconductive region of extrinsic Si infrared detectors. A simple theory is developed which predicts the transmissivity of such layers as a function of their sheet resistance and the wavelength of the radiation. Experimental data over the 2.5-20 µm wavelength and 5-500 Ω/square sheet resistance range are given for both diffused and ion-implanted layers and also for polysilicon gases. The temperature dependence of both transmissivity and sheet resistance is investigated from 20 to 300 K.

Free carrier absorption in silicon

Free carrier absorption in heavily doped layers reduces the useful photon flux in the photoconductive region of extrinsic Si infrared detectors. A simple theory is developed which predicts the transmissivity of such layers as a function of their sheet resistance and the wavelength of the radiation. Experimental data over the 2.5-20 /spl mu/m wavelength and 5-500 Omega/square sheet resistance range are given for both diffused and ion-implanted layers and also for polysilicon gates. The temperature dependence of both transmissivity and sheet resistance is investigated from 20 to 300 K.

Free Carrier Absorption in Silicon

This paper describes an experimental investigation on the infrared radiative properties of heavily doped Si at room temperature. Lightly doped Si wafers were ion-implanted with either boron or phosphorus atoms, with dosages corresponding to as-implanted peak doping concentrations of 10 20 and 10 21 cm -3 ; the peak doping concentrations after annealing are 3.1 × 10 19 and 2.8 × 10 20 cm -3 , respectively. Rapid thermal annealing was performed to activate the implanted dopants. A Fourier-transform infrared spectrometer was employed to measure the transmittance and reflectance of the samples in the wavelength range from 2 μm to 20 μm. Accurate carrier mobility and ionization models were identified after carefully reviewing the available literature, and then incorporated into the Drude model to predict the dielectric function of doped Si. The radiative properties of doped Si samples were calculated by treating the doped region as multilayer thin films of different doping concentrations on a thick lightly doped Si substrate. The measured spectral transmittance and reflectance agree well with the model predictions. The knowledge gained from this study will aid future design and fabrication of doped Si microstructures as wavelength selective emitters and absorbers in the midinfrared region.

Infrared Radiative Properties of Heavily Doped Silicon at Room Temperature

Transmission measurements are reported on highly phosphorous-doped n-type Si, at three different temperatures 300, 85, and 35°K, and for carrier densities ranging from 6 × 1018 to 4.9 × 1020 cm−3. Below the fundamental energy gap, the data are analysed in terms of three different processes: free carrier absorption, indirect transitions including the phonon contribution as well as the impurity or electron—electron scattering, and interconduction-band transitions. The absorption band due to inter-conduction-band transitions is observed to shift to higher wavelengths, when the doping increases. An explanation is given, taking into account the rise of the Fermi level in the conduction band.



Es werden Transmissionsmessungen an mit Phosphor hochdotiertem, n-leitendem Si mitgeteilt, die bei drei verschiedenen Temperaturen, 300, 85 und 35°K, fur Ladungstragerdichten zwischen 6 × 1018 und 4,9 × 1020 cm−3 durchgefuhrt wurden. Unterhalb der Grundgitterkante werden die Ergebnisse mit drei verschiedenen Prozessen diskutiert: freie Ladungstragerabsorption, indirekte Ubergange, die sowohl den Beitrag der Phononen als auch Defekt- oder Elektron–Elektron-Streuung einschliesen und Interleitungsband-Ubergange. Es wird beobachtet, das die Absorptionsbande, die durch die Interleitungsband-Ubergange verursacht wird, sich mit steigender Dotierung zu langeren Wellenlangen verschiebt. Es wird eine Erklarung gegeben, die den Anstieg des Ferminiveaus im Leitungsband berucksichtigt.

L. E. Howarth

Papers

Determination of Free Electron Effective Mass of n‐Type Silicon