H. P. Wei

Electron effective mass and band‐gap dependence on alloy composition of AlyGaxIn1−y−xAs, lattice matched to InP

AlyGaxIn1−y−xAs structures were prepared by molecular beam epitaxy to determine both the electron effective mass and band‐gap dependence of the InP lattice‐matched alloy. Cyclotron resonance and photoluminescence measurements were used, respectively. The effective mass obtained after nonparabolicity correction is m*=0.0403+0.0817y. The band‐gap relationships obtained at 300 and 5.5 K are Eg (eV)=0.752+1.453y, and Eg (eV)=0.792+1.530y, respectively.

Critical exponent in the fractional quantum Hall effect

Abstract We report the observation of a universal critical exponent in the fractional quantum Hall effect (FQHE) from a study of the temperature (T) dependent electron transport in between Landau level filling factors v = 2 5 and v = 1 3 , over a T range from 1.2 K to 22 mK. in an AlGaAs-GaAs heterostructure. Specifically, the maximum value of dp xy dB and the width of pxx show the same power law dependence on T, i.e. ~T−K. The critical exponent K=0.43 ± 0.02.This power law dependence is the same as that obtained in the integral quantum Hall effect (IQHE) [Wei et al., Phys. Rev. Lett. 61 (1988) 1294], in analogy to which our result indicates the existence of a divergent correlation length for the wavefunction of the quasi-particles in the FQHE for 1 3 2 5 . The localization to delocalization transition can be characterized by a universal critical exponent, k, in both the IQHE and the FQHE.

Persistent photoconductivity and the quantized Hall effect in In0.53Ga0.47As/InP heterostructures

A persistent photoconductivity is observed in the transport of the high mobility two‐dimensional electron gas in In0.53Ga0.47 As/InP heterostructures. Low field Hall measurements from 300 to 4.2 K and the quantized Hall effect in the high field limit are studied with radiation from visible and infrared light‐emitting diodes. Our results demonstrate conclusively that the effect is due to photogeneration of electron‐hole pairs in the heterostructure and trapping of holes in the In0.53Ga0.47 As.

New results on scaling in the integral quantum Hall effect

We report two new results, from temperature dependent transport measurements in two In0.53Ga0.47As/InP heterostructures, concerning the scaling of electronic transport in the integral quantum Hall effect. First, in a sample which has spin resolved Landau levels N=0↓, 1↓, 1↑, we find that the extrema of dρxydB, d2ρxxdB2 and d3ρ xydB3 in all spin-split Landau levels diverge like T−α, with a=K, 2K, 3K respectively. The exponent, k=0.42 ± 0.04, uniquely describes the localization to delocalization transition. Moreover, by generalizing these results to higher order derivatives of the transport coefficients ρ, we find that Δρ((B)−ρ(B∗)) are invariant under a length scale transformation. Second, in a sample with lower mobility the spin splitting for the N=1 Landau level is not resolved for T>60 mK, we find that both dρxydB(B∗) and 1ΔB in the N=1 Landau level diverge as T−K2 for 60 mK < T < 2.5 K. On the other hand, both quantities follow T−K for the spin-split N=0↓ Landau level.

Cyclotron mass of two‐dimensional holes in strained‐layer GaAs/In0.20Ga0.80As/GaAs quantum well structures

We report a systematic study of the effective mass of two‐dimensional (2D) holes in a series of ten p‐type GaAs/In0.20Ga0.80As/GaAs quantum well structure samples. The 2D hole density and its effective mass (m*)are independently determined from Shubnikov–de Haas and cyclotron resonance measurements at 4.2 K. We find the m* increases from (0.123±0.005) me to (0.191±0.015) me as the 2D hole density is varied from 0.54×1011/cm2to 8.5×1011/cm2. The experimental data are described quantitatively in terms of a two‐band tight binding model using the valence band edge mass and strain‐induced valence band splitting as parameters.

First observation of quantum Hall effect in a GaInAsP‐InP heterostructure grown by metalorganic vapor deposition

We report the first observation of quantum Hall effect in a Ga0.25In0.75As0.5P0.5 heterostructure grown by metalorganic chemical vapor deposition growth technique.

An experimental test of two-parameter scaling of integral quantum Hall effect

Abstract Detailed measurements are made of the temperature and magnetic field dependences of the magneto-transport coefficients, σ xx and σ xy , in an In 0.53 Ga 0.47 AsInP heterostructure to test the (two-parameter) renormalization group theory of the integral quantum Hall effect.

Transport studies of GaAs1−xSbx‐AlyGa1−yAs strained‐layer superlattices

Electrical transport in modulation‐doped GaAs1−xSbx‐AlyGa1−yAs strained‐layer superlattices (SLS) grown by molecular beam epitaxy was studied, using low field Hall measurements from 4.2 to 300 K, high field quantum transport, and the far‐infrared cyclotron resonance at 4.2 K. Our results show directly a degenerate two‐dimensional electron gas in the SLS with an effective mass m*=0.063m0 and a mobility μ=7.7×103 cm2/Vs at a density ns =6.7×1011 cm−2, demonstrating the feasibility of high quality GaAs1−xSbx‐AlyGa1−yAs SLS with good two‐dimensional electronic transport properties despite the large lattice mismatch between the constituent layers.

Universality and Scaling of Electronic Transport in the Integral Quantum Hall Effect

Quantitative experimental results are obtained on the electronic transport in the integral quantum Hall effect in InGaAs/InP heterojunctions. Both the maximum of dρ xy /dB and the inverse of the half width for ρ xx diverge like ~T −k We obtain k = 0.42 ± 0.04, independent of the Landau level index. These results confirm the prediction of the scaling theory that the characteristic power law behavior in the transport coefficients is a universal feature of delocalization in the integral quantum Hall effect.